[net] feeler connections can be made to outbound peers in same netgroup

Fixes a bug where feelers could be stuck trying to resolve a collision in the
tried table that is to an address in the same netgroup as an existing outbound peer.

Thanks to Muoi Tran for the original bug report and detailed debug logs to track
this down.

src/net.cpp

@@ -1765,9 +1765,15 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
                 addr = addrman.Select(fFeeler);
             }
 
+            // Require outbound connections to be to distinct network groups
+            if (!fFeeler && setConnected.count(addr.GetGroup())) {
+                break;
+            }
+
             // if we selected an invalid address, restart
-            if (!addr.IsValid() || setConnected.count(addr.GetGroup()) || IsLocal(addr))
+            if (!addr.IsValid() || IsLocal(addr)) {
                 break;
+            }
 
             // If we didn't find an appropriate destination after trying 100 addresses fetched from addrman,
             // stop this loop, and let the outer loop run again (which sleeps, adds seed nodes, recalculates