mac80211: don't fiddle with netdev queues in MLME code

The netdev queues should always represent the state that
the driver gave them, so fiddling with them isn't really
appropriate in the mlme code. Also, since we stop queues
for flushing now, this really isn't necessary any more.

As the scan/offchannel code has also been modified to no
longer do this a while ago, remove the outdated smp_mb()
and comments about it.

While at it, also add a pair of braces that was missing.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>