iwlwifi: always monitor for stuck queues

If we only monitor while associated, the following
can happen:
 - we're associated, and the queue stuck check
   runs, setting the queue "touch" time to X
 - we disassociate, stopping the monitoring,
   which leaves the time set to X
 - almost 2s later, we associate, and enqueue
   a frame
 - before the frame is transmitted, we monitor
   for stuck queues, and find the time set to
   X, although it is now later than X + 2000ms,
   so we decide that the queue is stuck and
   erroneously restart the device

It happens more with P2P because there we can
go between associated/unassociated frequently.

Cc: stable@vger.kernel.org
Reported-by: Ben Cahill <ben.m.cahill@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>