Send UDP packets to multicast address rather than broadcast address (#6331)

A smart router or switch is able to snoop the multicast address to
only send the packets to nodes listening on the multicast address.

Before all machines reachable on the L2 layer would receive the packet.

src/mesh/udp/UdpMulticastThread.h

@@ -56,7 +56,7 @@ class UdpMulticastThread : public concurrency::OSThread
         LOG_DEBUG("Broadcasting packet over UDP (id=%u)", mp->id);
         uint8_t buffer[meshtastic_MeshPacket_size];
         size_t encodedLength = pb_encode_to_bytes(buffer, sizeof(buffer), &meshtastic_MeshPacket_msg, mp);
-        udp.broadcastTo(buffer, encodedLength, UDP_MULTICAST_DEFAUL_PORT);
+        udp.writeTo(buffer, encodedLength, udpIpAddress, UDP_MULTICAST_DEFAUL_PORT);
         return true;
     }