Add portnum definition for ATAK Forwarder

portnums.proto

@@ -88,4 +88,7 @@ enum PortNum {
     /** Private applications should use portnums >= 256.  To simplify initial development and testing you can use "PRIVATE_APP"
      in your code without needing to rebuild protobuf files (via bin/regin_protos.sh) */
     PRIVATE_APP = 256;
+
+    /** ATAK Forwarder Plugin https://github.com/paulmandal/atak-forwarder */
+    ATAK_FORWARDER = 257;
   }