mac80211: reschedule sched scan after HW restart

Keep the sched scan req when starting sched scan, and reschedule
it in case of HW restart during sched scan.
The upper layer don't have to know about the restart.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>