Fix PNO restart flow

Fix PNO restart flow

PNO is sometimes restarted due to changes in scan parameters
(e.g., selected network changed or MAC randomization being
 enabled/disabled). Restart is done by stopping PNO and immediately
starting it again. This may result in the SCHED_SCAN_STOPPED event being
received after the request for new PNO, which will make wpa_supplicant
believe PNO is not active although it is actually is. As a result, the
next request to start PNO will fail because PNO is active and should be
stopped first.

Fix this by deferring the request to start PNO until the
SCHED_SCAN_STOPPED event is received in case sched_scan is being
stopped.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>