mac80211: fix notify_mac function

The ieee80211_notify_mac() function uses ieee80211_sta_req_auth() which
in turn calls ieee80211_set_disassoc() which calls a few functions that
need to be able to sleep, so ieee80211_notify_mac() cannot use RCU
locking for the interface list and must use rtnl locking instead.

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