can: Network Drop Monitor: Make use of consume_skb() in af_can.c

Since commit ead2ceb0 ("Network Drop
Monitor: Adding kfree_skb_clean for non-drops and modifying
end-of-line points for skbs") so called end-of-line points for skb's
should use consume_skb() to free the socket buffer.

In opposite to consume_skb() the function kfree_skb() is intended to
be used for unexpected skb drops e.g. in error conditions that now can
trigger the network drop monitor if enabled.

This patch moves the skb end-of-line point in af_can.c to use
consume_skb().

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>