can: add ability to allocate CANFD frame in skb data

This patch adds the ability of allocating a CANFD frame data structure in the
skb data area.

Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>