message: mission: only set gimbal protocol once
  Otherwise we keep setting this if the gimbal_manager_information message
  is sent again.
diff: @@ -106,10 +106,12 @@ void MissionImpl::process_mission_item_reached(const mavlink_message_t& message)
  void MissionImpl::process_gimbal_manager_information(const mavlink_message_t& message)
  {
  UNUSED(message);
  + if (_gimbal_protocol_cookie != nullptr) {
  LogDebug() << "Using gimbal protocol v2";
  _gimbal_protocol = GimbalProtocol::V2;
  _parent->unregister_timeout_handler(_gimbal_protocol_cookie);
  }
  +}
  void MissionImpl::wait_for_protocol()
  {
  @@ -128,6 +130,7 @@ void MissionImpl::receive_protocol_timeout()
  {
  LogDebug() << "Falling back to gimbal protocol v1";
  _gimbal_protocol = GimbalProtocol::V1;
  + _gimbal_protocol_cookie = nullptr;
  }
  Mission::Result MissionImpl::upload_mission(const Mission::MissionPlan& mission_plan)
  