can: raw: add CAN XL support

can: raw: add CAN XL support

Enable CAN_RAW sockets to read and write CAN XL frames analogue to the
CAN FD extension (new CAN_RAW_XL_FRAMES sockopt).

A CAN XL network interface is capable to handle Classical CAN, CAN FD and
CAN XL frames. When CAN_RAW_XL_FRAMES is enabled, the CAN_RAW socket checks
whether the addressed CAN network interface is capable to handle the
provided CAN frame.

In opposite to the fixed number of bytes for
- CAN frames (CAN_MTU = sizeof(struct can_frame))
- CAN FD frames (CANFD_MTU = sizeof(struct can_frame))
the number of bytes when reading/writing CAN XL frames depends on the
number of data bytes. For efficiency reasons the length of the struct
canxl_frame is truncated to the needed size for read/write operations.
This leads to a calculated size of CANXL_HDR_SIZE + canxl_frame::len which
is enforced on write() operations and guaranteed on read() operations.

NB: Valid length values are 1 .. 2048 (CANXL_MIN_DLEN .. CANXL_MAX_DLEN).

Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20220912170725.120748-8-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>