message: use system status from setter function
diff: @@ -623,7 +623,7 @@ void MavsdkImpl::send_heartbeat()
  MAV_AUTOPILOT_INVALID,
  get_own_component_id() == MAV_COMP_ID_AUTOPILOT1 ? _base_mode.load() : 0,
  get_own_component_id() == MAV_COMP_ID_AUTOPILOT1 ? _custom_mode.load() : 0,
  - 0);
  + get_system_status());
  send_message(message);
  }
  