AP_NavEKF: reduce height at which nav gain reduction starts
AC_AttitudeControl: Scale angle demand noise filter

Scales filter frequency using EKF nav gain scaler to take advantage of the reduced nav frequency whichcan tolerate a slower angle response.
This is required to reduce the effect of EKF optical flow noise increase with height.
AP_NavEKF: Increase height at which nav gain reduction starts

Compensates for optical flow induced noise increase with height.