udp-multicast: do not listen for incoming udp multicast packets if disabled (#6397)

Currently the config flag only control if packets are sent, not received.

As we discussed in VC this is not what was intended.

src/mesh/wifi/WiFiAPClient.cpp

@@ -133,7 +133,7 @@ static void onNetworkConnected()
     }
 
 #if HAS_UDP_MULTICAST
-    if (udpThread) {
+    if (udpThread && config.network.enabled_protocols & meshtastic_Config_NetworkConfig_ProtocolFlags_UDP_BROADCAST) {
         udpThread->start();
     }
 #endif