Merge bitcoin/bitcoin#30043: net: Replace libnatpmp with built-in PCP+NATPMP implementation

5c7cacf649a6b474b876a7d219c7dc683a25e33d ci: Remove natpmp build option and libnatpmp dependency (laanwj)
7e7ec984da50f45491b994aaab180e7735ad1d8f doc: Remove mention of natpmp build options (laanwj)
061c3e32a26c6c04bf734d62627403758d7e51d9 depends: Drop natpmp and associated option from depends (laanwj)
20a18bf6aa38e87f72e2645482d00d0c77a344f5 build: Drop libnatpmp from build system (laanwj)
7b04709862f48e9020c7bef79cb31dd794cf91d0 qt: Changes for built-in PCP+NAT-PMP (laanwj)
52f8ef66c61b82457a161f3b90cc87f57d1dda80 net: Replace libnatpmp with built-in NATPMP+PCP implementation in mapport (laanwj)
97c97177cdb2f596aa7d4a65c4bde87de50a96f2 net: Add PCP and NATPMP implementation (laanwj)
d72df63d16941576b3523cfeaa49985cf3cd4d42 net: Use GetLocalAddresses in Discover (laanwj)
e02030432b77abbf27bb4f67d879d3ad6d6366e6 net: Add netif utility (laanwj)
754e4254388ec8ac1be6cf807bf300cd43fd3da5 crypto: Add missing WriteBE16 function (laanwj)

Pull request description:

  Continues #30005. Closes #17012..

  This PR adds PCP (Port Control Protocol) from [RFC6887](https://datatracker.ietf.org/doc/html/rfc6887).  This adds, in addition to the existing IPv4 port mapping (which now uses PCP, with fallback to NAT-PMP), support for IPv6 pinholing-that is, opening a port on the firewall to make it reachable.

  PCP, like NAT-PMP is a simple UDP-based protocol, and the implementation is self-contained, so this gets rid of lthe libnatpnp dependency without adding a new one. It should otherwise be a drop-in replacement. NAT-PMP fallback is implemented so this will not make router support worse.

  For now it is disabled by default, though in the future (not in this PR) we could consider enable it by default to increase the number of connectable nodes without adding significant attack surface.

  To test:
  ```bash
  bitcoind -regtest -natpmp=1 -debug=net
  ```

  (most of the changes in this PR are, ironically, removing the libnatpmp dependency and associated build system and build docs)

  ## TODO

  - [x] Default gateway discovery on Linux / FreeBSD
  - [x] Default gateway discovery on Windows
  - [x] Default gateway discovery on MacOS
  - [x] Either solve FreeBSD compile issue (probably upstream issue) or remove FreeBSD support

  ## Things to consider for follow-up PRs

  - https://github.com/bitcoin/bitcoin/pull/30043#discussion_r1658764974 avoid unreachable nets (not given to -onlynet=)

  - https://github.com/bitcoin/bitcoin/pull/30043#discussion_r1658949236 could announce an addr:port where we do not listen (no -bind)

  - https://github.com/bitcoin/bitcoin/pull/30043#discussion_r1684368824 could announce the wrong port because it uses GetListenPort()

  - https://github.com/bitcoin/bitcoin/pull/30043#discussion_r1679709347 if we requested one port but another was assigned, then which one to use in the renewal?

  - https://github.com/bitcoin/bitcoin/pull/30043#discussion_r1772017020 Use `GetAdapterAddresses` to discover local addresses for Windows

ACKs for top commit:
  Sjors:
    ACK 5c7cacf649a6b474b876a7d219c7dc683a25e33d
  achow101:
    ACK 5c7cacf649a6b474b876a7d219c7dc683a25e33d
  vasild:
    ACK 5c7cacf649a6b474b876a7d219c7dc683a25e33d

Tree-SHA512: e35b69e56d5f5449a3d48a799f9b7b65107c65eeb3e245c2c1e9d42221e469ca5ead90afae423160601cd664dd553a51c859e04f4492f335b064aae3bf23e3bc

5 files changed, 7 insertions, 19 deletions

diff --git a/doc/build-freebsd.md b/doc/build-freebsd.md
index 6a25e9a834..8b3b10ab85 100644
--- a/doc/build-freebsd.md
+++ b/doc/build-freebsd.md
@@ -42,7 +42,7 @@ from ports. However, you can build DB 4.8 yourself [using depends](/depends).
 
 ```bash
 pkg install gmake
-gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_NATPMP=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
+gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
 ```
 
 When the build is complete, the Berkeley DB installation location will be displayed:
diff --git a/doc/build-openbsd.md b/doc/build-openbsd.md
index fafc91fc5f..908b750a8f 100644
--- a/doc/build-openbsd.md
+++ b/doc/build-openbsd.md
@@ -44,7 +44,7 @@ from ports. However you can build it yourself, [using depends](/depends).
 Refer to [depends/README.md](/depends/README.md) for detailed instructions.
 
 ```bash
-gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_NATPMP=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
+gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
 ...
 to: /path/to/bitcoin/depends/*-unknown-openbsd*
 ```
diff --git a/doc/build-osx.md b/doc/build-osx.md
index 600eebb6ff..c7cc84d42d 100644
--- a/doc/build-osx.md
+++ b/doc/build-osx.md
@@ -135,17 +135,6 @@ Skip if you do not need this functionality.
 brew install miniupnpc
 ```
 
-###### libnatpmp
-
-libnatpmp may be used for NAT-PMP port mapping.
-Skip if you do not need this functionality.
-
-``` bash
-brew install libnatpmp
-```
-
-Check out the [further configuration](#further-configuration) section for more information.
-
 ---
 
 #### ZMQ Dependencies
diff --git a/doc/build-unix.md b/doc/build-unix.md
index 4c3c659bff..086731be5a 100644
--- a/doc/build-unix.md
+++ b/doc/build-unix.md
@@ -60,9 +60,9 @@ executables, which are based on BerkeleyDB 4.8. Otherwise, you can build Berkele
 
 To build Bitcoin Core without wallet, see [*Disable-wallet mode*](#disable-wallet-mode)
 
-Optional port mapping libraries (see: `-DWITH_MINIUPNPC=ON` and `-DWITH_NATPMP=ON`):
+Optional port mapping library (see: `-DWITH_MINIUPNPC=ON`):
 
-    sudo apt install libminiupnpc-dev libnatpmp-dev
+    sudo apt install libminiupnpc-dev
 
 ZMQ dependencies (provides ZMQ API):
 
@@ -112,9 +112,9 @@ are based on Berkeley DB 4.8. Otherwise, you can build Berkeley DB [yourself](#b
 
 To build Bitcoin Core without wallet, see [*Disable-wallet mode*](#disable-wallet-mode)
 
-Optional port mapping libraries (see: `-DWITH_MINIUPNPC=ON` and `-DWITH_NATPMP=ON`):
+Optional port mapping library (see: `-DWITH_MINIUPNPC=ON`):
 
-    sudo dnf install miniupnpc-devel libnatpmp-devel
+    sudo dnf install miniupnpc-devel
 
 ZMQ dependencies (provides ZMQ API):
 
@@ -153,7 +153,7 @@ The legacy wallet uses Berkeley DB. To ensure backwards compatibility it is
 recommended to use Berkeley DB 4.8. If you have to build it yourself, and don't
 want to use any other libraries built in depends, you can do:
 ```bash
-make -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_NATPMP=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
+make -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
 ...
 to: /path/to/bitcoin/depends/x86_64-pc-linux-gnu
 ```
diff --git a/doc/dependencies.md b/doc/dependencies.md
index 4c620cf876..5789ea52f9 100644
--- a/doc/dependencies.md
+++ b/doc/dependencies.md
@@ -34,7 +34,6 @@ You can find installation instructions in the `build-*.md` file for your platfor
 ### Networking
 | Dependency | Releases | Version used | Minimum required | Runtime |
 | --- | --- | --- | --- | --- |
-| [libnatpmp](../depends/packages/libnatpmp.mk) | [link](https://github.com/miniupnp/libnatpmp/) | commit [f2433be...](https://github.com/bitcoin/bitcoin/pull/29708) | | No |
 | [MiniUPnPc](../depends/packages/miniupnpc.mk) | [link](https://miniupnp.tuxfamily.org/) | [2.2.7](https://github.com/bitcoin/bitcoin/pull/29707) | 2.1 | No |
 
 ### Notifications