vehicle_control_mode needs to be updated when offboard_control_mode is changed

[okalachev]

For dynamic flights in OFFBOARD mode it's necessary to switch between position/velocity/attitude/rates submodes fast.

For now, changes is offboard_control_mode topic does not trigger Commander to update the status, so the vehicle_control_mode doesn't get updated, causing delays (0.1–0.2 s) for publishing appropriate setpoints.

Like in this log, where automatic flip is performed (notice the delay between offboard_control_mode and vehicle_control_mode updates):

https://logs.px4.io/plot_app?log=fd5ad882-c4fb-49cc-9713-9201a6ee1379

This fix makes updates simultaneous:

https://logs.px4.io/plot_app?log=8c115337-4469-4de3-8490-33d619d66d21

These logs are from SITL, but we experienced the same on real hardware. In v1.8.2 it was making automatic flips impossible, without ugly hacks to switch to position control earlier to compensate the possible delay.

@dagar