Merge branch 'ipv4-fib-remove-rtnl-in-fib_net_exit_batch'

Kuniyuki Iwashima says:

====================
ipv4: fib: Remove RTNL in fib_net_exit_batch().

Currently, we flush all IPv4 routes at ->exit_batch() during
netns dismantle, which requires an extra RTNL.

IPv4 routes are not added from the fast path unlike IPv6, so
we can flush routes before default_device_exit_batch().

However, there is implicit ordering between ip_fib_net_exit()
and default_device_exit_batch().

This series detangles it and moves ip_fib_net_exit() to
 ->exit_rtnl() to save the RTNL dance.

The same change for IPv6 will need more work.
====================

Link: https://patch.msgid.link/20260612063225.455191-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>