- update sanity checks
- add DLC to length conversion helpers
  - can_dlc2len() - get data length from can_dlc with sanitized can_dlc
  - can_len2dlc() - map the sanitized data length to an appropriate DLC
Signed-off-by: NOliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>