ipmr: Use rtnl_register_many().

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

When it succeeds for built-in callers, rtnl_register_many() guarantees
all rtnetlink types in the passed array are supported, and there is no
chance that a part of message types is not supported.

Let's use rtnl_register_many() instead.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241014201828.91221-9-kuniyu@amazon.com


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