message: mission: don't set yaw to 0
diff: @@ -611,7 +611,7 @@ void MissionImpl::assemble_mavlink_messages()
  mission_item_impl.get_loiter_time_s(), // loiter time in seconds
  NAN, // empty
  0.0f, // radius around waypoint in meters ?
  - 0.0f, // loiter at center of waypoint
  + NAN, // don't change yaw
  last_x,
  last_y,
  last_z,
  