can: dev: add can_is_canfd_skb() API

The CAN device drivers can use can_is_canfd_skb() to check if the frame to send
is on CAN FD mode or normal CAN mode.
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Dong Aisheng <b29396@freescale.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

include/linux/can/dev.h

@@ -99,6 +99,12 @@ static inline int can_dropped_invalid_skb(struct net_device *dev,
 	return 1;
 }
 
+static inline bool can_is_canfd_skb(const struct sk_buff *skb)
+{
+	/* the CAN specific type of skb is identified by its data length */
+	return skb->len == CANFD_MTU;
+}
+
 /* get data length from can_dlc with sanitized can_dlc */
 u8 can_dlc2len(u8 can_dlc);