can: gs_usb: document the USER_ID feature

The widely used open source firmware candleLight has optional support
for reading/writing of an user defined value into the device's flash.

This is indicated by the GS_CAN_FEATURE_USER_ID feature. The
corresponding request are GS_USB_BREQ_GET_USER_ID and
GS_USB_BREQ_SET_USER_ID.

This patch documents these values.

Link: https://lore.kernel.org/all/20220309124132.291861-11-mkl@pengutronix.de
Link: https://github.com/candle-usb/candleLight_fw/commit/1453d70dc9a9d98ac254893ba5114b8e826e0e39
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -40,6 +40,8 @@ enum gs_usb_breq {
 	GS_USB_BREQ_DEVICE_CONFIG,
 	GS_USB_BREQ_TIMESTAMP,
 	GS_USB_BREQ_IDENTIFY,
+	GS_USB_BREQ_GET_USER_ID,
+	GS_USB_BREQ_SET_USER_ID,
 };
 
 enum gs_can_mode {
@@ -94,6 +96,7 @@ struct gs_device_config {
 #define GS_CAN_MODE_ONE_SHOT BIT(3)
 #define GS_CAN_MODE_HW_TIMESTAMP BIT(4)
 /* GS_CAN_FEATURE_IDENTIFY BIT(5) */
+/* GS_CAN_FEATURE_USER_ID BIT(6) */
 
 struct gs_device_mode {
 	__le32 mode;
@@ -124,6 +127,7 @@ struct gs_identify_mode {
 #define GS_CAN_FEATURE_ONE_SHOT BIT(3)
 #define GS_CAN_FEATURE_HW_TIMESTAMP BIT(4)
 #define GS_CAN_FEATURE_IDENTIFY BIT(5)
+#define GS_CAN_FEATURE_USER_ID BIT(6)
 
 struct gs_device_bt_const {
 	__le32 feature;