can: slcan: Replace sizeof struct can_frame with CAN_MTU

Use CAN_MTU macro instead of sizeof(struct can_frame) just like the
other drivers do.

Signed-off-by: Marek Vasut <[e-mail]>
Cc: Oliver Hartkopp <[e-mail]>
Cc: Marc Kleine-Budde <[e-mail]>
Signed-off-by: Marc Kleine-Budde <[e-mail]>

drivers/net/can/slcan.c

···
 {
 	struct slcan *sl = netdev_priv(dev);
 
-	if (skb->len != sizeof(struct can_frame))
+	if (skb->len != CAN_MTU)
 		goto out;
 
 	spin_lock(&sl->lock);
···
 	dev->addr_len		= 0;
 	dev->tx_queue_len	= 10;
 
-	dev->mtu		= sizeof(struct can_frame);
+	dev->mtu		= CAN_MTU;
 	dev->type		= ARPHRD_CAN;
 
 	/* New-style flags. */