message: offboard: add missing mutex
diff: @@ -32,7 +32,10 @@ void OffboardImpl::init()
  void OffboardImpl::deinit()
  {
  + {
  + std::lock_guard<std::mutex> lock(_mutex);
  stop_sending_setpoints();
  + }
  _parent->unregister_all_mavlink_message_handlers(this);
  }
  