message: Handle MAV_CMD_NAV_LOITER_TIME (QGC Mission import)
  Importer was not identifying `MAV_CMD_NAV_LOITER_TIME`. This commit
  adds support for `MAV_CMD_NAV_LOITER_TIME` while importing QGC Mission.
diff: @@ -969,6 +969,7 @@ MissionImpl::compose_mission_items_from_json(Mission::mission_items_t &mission_i
  // Parameters of Mission item & MAV command of it.
  float speed_m_s = 0.f;
  float gimbal_pitch_deg = 0.f, gimbal_yaw_deg = 0.f;
  + float loiter_time_s = 0.f;
  bool is_fly_through = false;
  double lat_deg = NAN, lon_deg = NAN, rel_alt_deg = NAN;
  double photo_interval = 0.;
  @@ -1002,6 +1003,9 @@ MissionImpl::compose_mission_items_from_json(Mission::mission_items_t &mission_i
  gimbal_pitch_deg = params[0]; // Pitch value is -ve as its in NED frame.
  gimbal_yaw_deg = params[2];
  break;
  + case MAV_CMD_NAV_LOITER_TIME:
  + loiter_time_s = params[0];
  + // FALLTHROUGH
  case MAV_CMD_NAV_WAYPOINT:
  is_fly_through = (params[0] == 0.0) ? true : false;
  // FALLTHROUGH
  @@ -1036,6 +1040,9 @@ MissionImpl::compose_mission_items_from_json(Mission::mission_items_t &mission_i
  if (photo_interval) {
  new_item->set_camera_photo_interval(photo_interval);
  }
  + if (loiter_time_s) {
  + new_item->set_loiter_time(loiter_time_s);
  + }
  new_item->set_camera_action(camera_action);
  return new_item;
  }());
  