WPS: Add 'wpa_cli wps_pin get' for generating random PINs

This can be used, e.g., in a UI to generate a PIN without
starting WPS (or P2P) operation.

wpa_supplicant/README-WPS

@@ -127,6 +127,11 @@ This starts the WPS negotiation in the same way as above with the
 generated PIN.
 
 
+If a random PIN is needed for a user interface, "wpa_cli wps_pin get"
+can be used to generate a new PIN without starting WPS negotiation.
+This random PIN can then be passed as an argument to another wps_pin
+call when the actual operation should be started.
+
 If the client design wants to support optional WPS PBC mode, this can
 be enabled by either a physical button in the client device or a
 virtual button in the user interface. The PBC operation requires that

wpa_supplicant/ctrl_iface.c

@@ -340,7 +340,10 @@ static int wpa_supplicant_ctrl_iface_wps_pin(struct wpa_supplicant *wpa_s,
 
 	if (os_strcmp(cmd, "any") == 0)
 		_bssid = NULL;
-	else if (hwaddr_aton(cmd, bssid)) {
+	else if (os_strcmp(cmd, "get") == 0) {
+		ret = wps_generate_pin();
+		goto done;
+	} else if (hwaddr_aton(cmd, bssid)) {
 		wpa_printf(MSG_DEBUG, "CTRL_IFACE WPS_PIN: invalid BSSID '%s'",
 			   cmd);
 		return -1;
@@ -367,6 +370,7 @@ static int wpa_supplicant_ctrl_iface_wps_pin(struct wpa_supplicant *wpa_s,
 	if (ret < 0)
 		return -1;
 
+done:
 	/* Return the generated PIN */
 	ret = os_snprintf(buf, buflen, "%08d", ret);
 	if (ret < 0 || (size_t) ret >= buflen)