Add extended driver scan request command: driver_ops::scan2()

This can be used to provide support for scanning multiple SSIDs at a
time to optimize scan_ssid=1 operations. In addition, Probe Request IEs
will be available to scan2() (e.g., for WPS PBC scanning).

src/drivers/driver_test.c

@@ -1317,5 +1317,6 @@ const struct wpa_driver_ops wpa_driver_test_ops = {
 	wpa_driver_test_global_init,
 	wpa_driver_test_global_deinit,
 	wpa_driver_test_init2,
-	wpa_driver_test_get_interfaces
+	wpa_driver_test_get_interfaces,
+	NULL /* scan2 */
 };