commit 2171abc5
  Author: Johannes Berg <johannes@sipsolutions.net>
  Date:   Thu Oct 29 08:34:00 2009 +0100

      mac80211: fix addba timer

left a problem in there, even if the timer was
never started it could be deleted and then added.

Linus pointed out that del_timer_sync() isn't
actually needed if we make the timer able to
deal with no longer being needed when it gets
queued _while_ we're in the locked section that
also deletes it. For that the timer function only
needs to check the HT_ADDBA_RECEIVED_MSK bit as
well as the HT_ADDBA_REQUESTED_MSK bit, only if
the former is clear should it do anything.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>