can: gs_usb: document GS_CAN_FEATURE_GET_STATE

Document the new feature ("GS_CAN_FEATURE_GET_STATE") that indicates
that the state of the CAN controller can be queried with the new
GS_USB_BREQ_GET_STATE control message.

Signed-off-by: Jeroen Hofstee <jhofstee@victronenergy.com>
Link: https://lore.kernel.org/all/20221019221016.1659260-7-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>