mac80211: handle sched_scan_stopped vs. hw restart race

On hw restart, mac80211 might try to reconfigure already
stopped sched scan, if ieee80211_sched_scan_stopped_work()
wasn't scheduled yet.

This in turn will keep the device driver with scheduled scan
configured, while both mac80211 and cfg80211 will clear
their sched scan state once the work is scheduled.

Fix it by ignoring ieee80211_sched_scan_stopped() calls
while in hw restart, and flush the work before starting
the reconfiguration.

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>