* FlightTask: Fix ekf2 reset race condition during task switch
During a loss of GPS data when using GPS as primary height source,
the height is reset to baro and the local position gets invalid at the
same time. This triggers a switch to altitude flight task and a setpoint
reset.
This combination of events had the effect to ignore the height reset,
the large sudden height error could create an abrupt change of altitude
or even a crash.
The ekf2 reset is now done at the beginning of each update call.
Adjusting the tilt limit can lead to diverging position control
and should only be used by setting a sanity limit for the controller
and not to adjust during the descent phase of a Land or RTL.
Otherwise it leads to flyaways in important failsafe modes when
there's stronger disturbance e.g. wind.
Unfortunately the constraints cannot be implemented using the
_constraints because the controller uses that directly. This
causes discontinuities in the velocity and/or accel at various
points of the flight. In particular this was used in Takeoff.
Instead this was done by changing target accel/velocity in the
jerk-optimal velocity planner for Z.
