mac80211: fix todo lock

The key todo lock can be taken from different locks
that require it to be _bh to avoid lock inversion
due to (soft)irqs.

This should fix the two problems reported by Bob and
Gabor:
http://mid.gmane.org/20090619113049.GB18956@hash.localnet
http://mid.gmane.org/4A3FA376.8020307@openwrt.org

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Bob Copeland <me@bobcopeland.com>
Cc: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>