can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once

can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once

commit 8cb68751c115d176ec851ca56ecfbb411568c9e8 upstream.

If an invalid CAN frame is received, from a driver or from a tun
interface, a Kernel warning is generated.

This patch replaces the WARN_ONCE by a simple pr_warn_once, so that a
kernel, bootet with panic_on_warn, does not panic. A printk seems to be
more appropriate here.

Reported-by: syzbot+4386709c0c1284dca827@syzkaller.appspotmail.com
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[bwh: Backported to 3.2:
 - Keep using the 'drop' label, as it has another user
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>