net: move nLocalHostNonce to CConnman

This behavior seems to have been quite racy and broken.

Move nLocalHostNonce into CNode, and check received nonces against all
non-fully-connected nodes. If there's a match, assume we've connected
to ourself.

src/main.cpp

@@ -5025,7 +5025,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         // Disconnect if we connected to ourself
-        if (nNonce == nLocalHostNonce && nNonce > 1)
+        if (pfrom->fInbound && !connman.CheckIncomingNonce(nNonce))
         {
             LogPrintf("connected to self at %s, disconnecting\n", pfrom->addr.ToString());
             pfrom->fDisconnect = true;