can: gw: Use rtnl_register_many().

We will remove rtnl_register_module() in favour of rtnl_register_many().

rtnl_register_many() will unwind the previous successful registrations
on failure and simplify module error handling.

Let's use rtnl_register_many() instead.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241014201828.91221-11-kuniyu@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>