linux-wandboard

mac80211: disallow fixing bitrates with hw rate control

When hw rate control is used, these parameters have
no meaning because the hardware cannot get at them
right now, so disallow setting them. Also clean up
the function a bit.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>