VTOL goes into deadlock when in manual transition

[RomanBapst]

I can reproduce this in SITL on all three vehicle types:

When doing a transition in manual mode it can happen that the transition finishes but
the vtol_att_control module does not run anymore because it did not switch to polling on the fw actuator controls. It's pure luck if it works.

@dagar FYI

[dagar]

Ouch, I'll take a look this morning.