message: Ignore send_message when TCP connection is down
diff: @@ -130,6 +130,10 @@ ConnectionResult TcpConnection::stop()
  bool TcpConnection::send_message(const mavlink_message_t& message)
  {
  + if (!_is_ok) {
  + return false;
  + }
  +
  if (_remote_ip.empty()) {
  LogErr() << "Remote IP unknown";
  return false;
  