Wake message handling thread when we receive a new block

This forces the message handling thread to make another full
iteration of SendMessages prior to going back to sleep, ensuring
we announce the new block to all peers before sleeping.

src/net_processing.cpp

@@ -822,6 +822,7 @@ void PeerLogicValidation::UpdatedBlockTip(const CBlockIndex *pindexNew, const CB
                 }
             }
         });
+        connman->WakeMessageHandler();
     }
 
     nTimeBestReceived = GetTime();