vxcan: remove sk reference in peer skb

With can_create_echo_skb() the skb which is forwarded to the peer CAN
interface shares the sk pointer from the originating socket.
This makes the CAN frame show up in the peer namespace as a TX packet.

With the use of skb_clone() analogue to the handling in gw.c the peer
skb gets a new start in the peer namespace and correctly appears as
a RX packet.

Link: https://lore.kernel.org/all/20220309120416.83514-4-socketcan@hartkopp.net


Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>