We should warn user-space that it is doing something wrong when trying
to activate sessions with identical parameters but WARN_ON_ONCE macro
can not be used here as it serves a different purpose.

So it would be good to replace it with netdev_warn_once() message.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 9d71dd0c ("can: add support of SAE J1939 protocol")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/all/20220729143655.1108297-1-pchelkin@ispras.ru
[mkl: fix indention]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>