GCS_MAVLink: add common handling of mavlink command messages

libraries/GCS_MAVLink/GCS.h

@@ -273,6 +273,8 @@ protected:
     bool telemetry_delayed() const;
     virtual uint32_t telem_delay() const = 0;
 
+    MAV_RESULT handle_command_long_message(mavlink_command_long_t &packet);
+
 private:
 
     float       adjust_rate_for_stream_trigger(enum streams stream_num);

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1835,6 +1835,18 @@ void GCS_MAVLINK::handle_common_mission_message(mavlink_message_t *msg)
     }
 }
 
+MAV_RESULT GCS_MAVLINK::handle_command_long_message(mavlink_command_long_t &packet)
+{
+    MAV_RESULT result = MAV_RESULT_FAILED;
+
+    switch (packet.command) {
+    default:
+        result = MAV_RESULT_UNSUPPORTED;
+    }
+
+    return result;
+}
+
 GCS &gcs()
 {
     return *GCS::instance();