Drift mode broken in copter master

Lucas noticed that drift mode was pulsing the motors badly in master. I have reproduced the issue in the RealFlight sim, log here:
its fine in POSHOLD, LOITER and ALT_HOLD.
I assume its related to the AP_Motors change?

I can also reproduce in normal SITL if I raise SIM_BARO_RND to 0.5 so baro isn’t perfect.
Looks to be an issue in the get_throttle_assist() code

found it, the gain needs to be scaled by 1000x too. I’ve pushed a fix

We can use RealFlight for testing (sitl,hitl) now ?

@badzz, it isn’t publicly available yet, but I hope it will be soon