multiplexer: Don't retransmit AIS nmea0183 input

Author: leamas

model/src/multiplexer.cpp

@@ -252,6 +252,11 @@ void Multiplexer::HandleN0183(
       std::shared_ptr<const Nmea0183Msg> msg = n0183_msg;
       if ((m_legacy_input_filter_behaviour && !passes_input_filter) ||
           passes_input_filter) {
+        // Don't retransmit synthetic messages generated by AisDecoder or
+        // when sending to plugins using PushNMEABuffer()
+        if (n0183_msg->source && n0183_msg->source->iface == "virtual")
+          continue;
+
         //  Allow re-transmit on same port (if type is SERIAL),
         //  or any other NMEA0183 port supporting output
         //  But, do not echo to the source network interface.  This will