can: dev: add CAN XL support to virtual CAN

Make use of new can_skb_get_data_len() helper.
Add support for variable CANXL MTU using the new can_is_canxl_dev_mtu().

Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20220912170725.120748-7-socketcan@hartkopp.net


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