Restore previous wpa_state in scan-only result handler

Restore previous wpa_state in scan-only result handler

The SCAN TYPE=ONLY results do not trigger a connection operation
automatically. As such, there was no explicit operation that would
change wpa_state after such a scan-only operation and WPA_SCANNING state
could have been left in effect until the next operation is triggered by
an external command. This is not desirable, so restore the wpa_state
that was in use when the scan was started in case WPA_SCANNING state is
still set when the scan operation completes.

This was triggered by the following mac80211_hwsim test sequence:
dbus_wps_oom scan_trigger_failure

Signed-off-by: Jouni Malinen <j@w1.fi>