can: preserve skbuff protocol in can_put_echo_skb

The skbuff protocol value was formerly fixed/sanitized to ETH_P_CAN in
can_put_echo_skb(). With CAN FD this value has to be preserved.
This patch changes the hard assignment of the protocol value to a check of
valid protocol values for CAN and CAN FD.
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev.c

@@ -317,7 +317,9 @@ void can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 	BUG_ON(idx >= priv->echo_skb_max);
 
 	/* check flag whether this packet has to be looped back */
-	if (!(dev->flags & IFF_ECHO) || skb->pkt_type != PACKET_LOOPBACK) {
+	if (!(dev->flags & IFF_ECHO) || skb->pkt_type != PACKET_LOOPBACK ||
+	    (skb->protocol != htons(ETH_P_CAN) &&
+	     skb->protocol != htons(ETH_P_CANFD))) {
 		kfree_skb(skb);
 		return;
 	}
@@ -329,7 +331,6 @@ void can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 			return;
 
 		/* make settings for echo to reduce code in irq context */
-		skb->protocol = htons(ETH_P_CAN);
 		skb->pkt_type = PACKET_BROADCAST;
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 		skb->dev = dev;