[PATCH] mac80211: document a lot more

This patch adds a lot more documentation (in kernel-doc format)
to include/net/mac80211.h

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