Increase signal-to-noise ratio in debug.log by adjusting log level when logging failed non-manual connect():s

Before this patch:

```
$ src/bitcoind -printtoconsole
…
2018-02-28 18:42:51 UpdateTip: new best=0000000000005448b10a219683d34b770a28044e1cc421032dea1a79ff548948 height=1286903 version=0x20000000 log2_work=69.791313 tx=17408546 date='2018-02-28 18:42:46' progress=1.000000 cache=0.0MiB(173txo)
2018-02-28T18:37:52Z connect() 10.11.21.34:18333 failed after select(): Connection refused (111)
2018-02-28 18:43:22 connect() to 10.11.43.14:18333 failed after select(): Network is unreachable (101)
2018-02-28 18:44:49 UpdateTip: new best=000000000000029a521ff2803e1441b09413b876accff5084a4cccf7747d798b height=1286904 version=0x20000000 log2_work=69.791345 tx=17408559 date='2018-02-28 18:44:51' progress=1.000000 cache=0.1MiB(502txo)
2018-02-28 18:46:54 connect() to [2001:0:9d38:78ff:1234:1234:1234:1234]:18333 failed: Network is unreachable (101)
2018-02-28 18:48:56 connect() to [2001:0:9d38:6aff:1234:1234:1234:1234]:18333 failed: Network is unreachable (101)
2018-02-28 18:49:11 UpdateTip: new best=000000000000000206b79eb235e5dd907b6369de0e5d764330bf40ec0d460311 height=1286905 version=0x20000000 log2_work=69.791377 tx=17408577 date='2018-02-28 18:49:12' progress=1.000000 cache=1.0MiB(5245txo)
```

After this patch:

```
$ src/bitcoind -printtoconsole
…
2018-02-28 18:42:51 UpdateTip: new best=0000000000005448b10a219683d34b770a28044e1cc421032dea1a79ff548948 height=1286903 version=0x20000000 log2_work=69.791313 tx=17408546 date='2018-02-28 18:42:46' progress=1.000000 cache=0.0MiB(173txo)
2018-02-28 18:44:49 UpdateTip: new best=000000000000029a521ff2803e1441b09413b876accff5084a4cccf7747d798b height=1286904 version=0x20000000 log2_work=69.791345 tx=17408559 date='2018-02-28 18:44:51' progress=1.000000 cache=0.1MiB(502txo)
2018-02-28 18:49:11 UpdateTip: new best=000000000000000206b79eb235e5dd907b6369de0e5d764330bf40ec0d460311 height=1286905 version=0x20000000 log2_work=69.791377 tx=17408577 date='2018-02-28 18:49:12' progress=1.000000 cache=1.0MiB(5245txo)
```

Please note that "manual connect():s" (invoked via `-connect`, `-proxy` or `addnode`) are still reported as usual:

```
$ src/bitcoind -printtoconsole -connect=10.11.12.13
…
2018-02-28 18:33:13 connect() to 10.11.12.13:18333 failed after select(): Connection refused (111)
$ src/bitcoind -printtoconsole -proxy=10.11.12.13
…
2018-02-28 18:32:32 connect() to 10.11.12.13:9050 failed after select(): Connection refused (111)
$ src/bitcoind -printtoconsole &
$ src/bitcoin-cli addnode "10.11.12.13" onetry
…
2018-02-28 18:34:40 connect() to 10.11.12.13:18333 failed after select(): Connection refused (111)
```

1 files changed, 3 insertions, 3 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 33a60ac96e..01db30f908 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -367,7 +367,7 @@ static CAddress GetBindAddress(SOCKET sock)
     return addr_bind;
 }
 
-CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure)
+CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, bool manual_connection)
 {
     if (pszDest == nullptr) {
         if (IsLocal(addrConnect))
@@ -431,7 +431,7 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
             if (hSocket == INVALID_SOCKET) {
                 return nullptr;
             }
-            connected = ConnectSocketDirectly(addrConnect, hSocket, nConnectTimeout);
+            connected = ConnectSocketDirectly(addrConnect, hSocket, nConnectTimeout, manual_connection);
         }
         if (!proxyConnectionFailed) {
             // If a connection to the node was attempted, and failure (if any) is not caused by a problem connecting to
@@ -1991,7 +1991,7 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
     } else if (FindNode(std::string(pszDest)))
         return;
 
-    CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure);
+    CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, manual_connection);
 
     if (!pnode)
         return;