Add warning message for unknown Broker statuses

There's now a couple placeholder/unimplemented status values in Broker
related to upcoming routing features that we don't want to handle
explicitly for compatibility reasons, but also don't want the compiler
warning about unhandled values in the switch.

src/broker/Manager.cc

@@ -1229,6 +1229,10 @@ void Manager::ProcessStatus(broker::status stat)
 		--peer_count;
 		event = Broker::peer_lost;
 		break;
+
+	default:
+		reporter->Warning("Unhandled Broker status: %s", to_string(stat).data());
+		break;
 	}
 
 	if ( ! event )