cfg80211: process the max power on a country IE

The max power from each country IE triplet was being ignored.
This fix isn't critical as CRDA was always being used for the lower
limit, but we should process it in case the AP still wants to
decrease power output even more for whatever reason.

Reported-by: Benoit PAPILLAULT <benoit.papillault@free.fr>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>