mac80211: rework debug settings and make debugging safer

This patch reworks the mac80211 debug settings making them more focused
and adding help text for those that didn't have one. It also removes a
number of printks that can be triggered remotely and add no value, e.g.
"too short deauthentication frame received - ignoring".

If somebody really needs to debug that they should just add a monitor
interface and look at the frames in wireshark.

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