This makes minstrel the default rate control algorithm
for mac80211. For more information see:

http://wireless.kernel.org/en/developers/Documentation/mac80211/RateControl/minstrel

If someone can come up with a better algorithm they get a prize
(undisclosed).
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>