mac80211: use freezable workqueue for restart work

Requesting hw restart during suspend might result
in the restart work being executed after mac80211
and the hw are suspended.

Solve the race by simply scheduling the restart
work on a freezable workqueue.

Note that there can be some cases of reconfiguration
on resume (besides the hardware restart):

* wowlan is not configured -
    All the interfaces removed were removed on suspend,
    and drv_stop() was called. At this point the driver
    shouldn't expect for hw_restart anyway, so we can
    simply cancel it (on resume).

* wowlan is configured, drv_resume() == 1
    There is no definitive expected behavior in this case,
    as each driver might have different expectations (e.g.
    setting some flags on suspend/restart vs. not handling
    spurious recovery).
    For now, simply let the hw_restart work run again after
    resume, and hope the driver will handle it well (or at
    least initiate another hw restart).

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>