message: mission: ignore acks when we don't expect them
diff: @@ -158,6 +158,11 @@ void MissionImpl::process_mission_ack(const mavlink_message_t& message)
  return;
  }
  + if (_activity.state == Activity::State::NONE) {
  + LogWarn() << "Mission ack ignored";
  + return;
  + }
  +
  // We got some response, so it wasn't a timeout and we can remove it.
  _parent->unregister_timeout_handler(_timeout_cookie);
  