can: length: canfd_sanitize_len(): add function to sanitize CAN-FD data length

The data field in CAN-FD frames have specifig frame length (0, 1, 2, 3, 4, 5,
6, 7, 8, 12, 16, 20, 24, 32, 48, 64). This function "rounds" up a given length
to the next valid CAN-FD frame length.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-10-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

include/linux/can/length.h

@@ -45,4 +45,10 @@ u8 can_fd_dlc2len(u8 dlc);
 /* map the sanitized data length to an appropriate data length code */
 u8 can_fd_len2dlc(u8 len);
 
+/* map the data length to an appropriate data link layer length */
+static inline u8 canfd_sanitize_len(u8 len)
+{
+	return can_fd_dlc2len(can_fd_len2dlc(len));
+}
+
 #endif /* !_CAN_LENGTH_H */