Merge branch 'fib-rules-convert-rtm_newrule-and-rtm_delrule-to-per-netns-rtnl'

Kuniyuki Iwashima says:

====================
fib: rules: Convert RTM_NEWRULE and RTM_DELRULE to per-netns RTNL.

Patch 1 ~ 2 are small cleanup, and patch 3 ~ 8 make fib_nl_newrule()
and fib_nl_delrule() hold per-netns RTNL.

v1: https://lore.kernel.org/20250206084629.16602-1-kuniyu@amazon.com
====================

Link: https://patch.msgid.link/20250207072502.87775-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>