Add GCS option to change the L3GD20 rate
assert the return value
Merge pull request #971 from metropt/update_gyro_rate_ff3

Add GCS option to change the L3GD20 rate
[Airspeed]: Simplfied airspeed module by removing #ifdefs.
[Airspeed]: Enabled Eagle Tree airspeed sensor driver in most F3 and F4
targets.