Scan request failures are observed in wpa_supplicant debug log when
Android framework starts PNO scan in driver via ctrl interface command
'set pno 1' and wpa_supplicant also tries to issue a scan request after
PNO has started in the driver.
Some drivers may reject a normal scan request when PNO is already in
progress. wpa_supplicant should consider PNO status before issuing start
scan request to the driver. Otherwise, wpa_supplicant will get failures
from driver for the scan request and it will end up rescheduling scan
request in periodic interval and get a start scan request failure for
each attempt.
In order to avoid unnecessary scan attempt when PNO scan is already
running, PNO status is checked before issuing scan request to driver.