can: dev: let can_get_echo_skb() return dlc of CAN frame

can_get_echo_skb() is usually called in the TX complete handler.
The stats->tx_packets and stats->tx_bytes should be updated there, too.
This patch simplifies to figure out the size of the sent CAN frame.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index a0969fcb..5d2efe7 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -92,7 +92,7 @@
 
 void can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 		      unsigned int idx);
-void can_get_echo_skb(struct net_device *dev, unsigned int idx);
+unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx);
 void can_free_echo_skb(struct net_device *dev, unsigned int idx);
 
 struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf);