mac80211: stop queues before carrier off

mac80211: stop queues before carrier off

During testing of the disassociation fixes, Tomas noticed that it
was possible to run into a situation where you'd suddenly get a
few "wlan0: dropped frame to <AP> (unauthorized port)" messages
and I found this to be due to the AP's sta_info having been
removed but netif_carrier_off not having removed/stopped traffic
yet. To avoid that, stop the queue for the interface (and avoid
bringing them up when another vif scans when they weren't up.)

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