mac80211: fix lockdep warning

Since the introduction of the fixes for the
reorder timer, mac80211 will cause lockdep
warnings because lockdep confuses
local->skb_queue and local->rx_skb_queue
and treats their lock as the same.

However, their locks are different, and are
valid in different contexts (the former is
used in IRQ context, the latter in BH only)
and the only thing to be done is mark the
former as a different lock class so that
lockdep can tell the difference.

Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Reported-by: Sujith <m.sujith@gmail.com>
Reported-by: Miles Lane <miles.lane@gmail.com>
Tested-by: Sujith <m.sujith@gmail.com>
Tested-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>