wifi(vts): Ignore IWifi.stop() returning ERROR_NOT_AVAILABLE

When IWifi.stop() is invoked back to back (happens in the ConfigureChip
vts test), the HAL would return ERROR_NOT_AVAILABLE if the previous stop
is still being processed. This is not an error that needs to fail the test,
but a legitimate status for stop. We have a retry mechanism to handle
this in both the VTS test and framework for the case where IWifi.start()
is invoked while the previous stop is being processed.

While there, corrected a few log messages emitted by the HAL to debug
such startup/stop issues better.

Bug: 63971806
Test: `vts-tradefed run commandAndExit vts --skip-all-system-status-check
--primary-abi-only --skip-preconditions --module VtsHalWifiV1_0Target -l
INFO`

Change-Id: I5e3470ac97541a6ea10aceec9b737e5d03ed5206