Merge branch 'ipmr-no-rtnl-for-rtnl_family_ipmr-rtnetlink'

Kuniyuki Iwashima says:

====================
ipmr: No RTNL for RTNL_FAMILY_IPMR rtnetlink.

This series removes RTNL from ipmr rtnetlink handlers.

After this series, there are a few RTNL left in net/ipv4/ipmr.c
and such users will be converted to per-netns RTNL in another
series.

Patch 1 adds a selftest to exercise most? of the RTNL paths
 in net/ipv4/ipmr.c

Patch 2 - 6 converts RTM_GETLINK / RTM_GETROUTE handlers
 to RCU.

Patch 7 - 9 converts ->exit_batch() to ->exit_rtnl() to
 save one RTNL in cleanup_net().

Patch 10 - 11 removes unnecessary RTNL during setup_net()
 failure.

Patch 12 is a random cleanup.

Patch 13 - 15 drops RTNL for RTM_NEWROUTE and RTM_DELROUTE.
====================

Link: https://patch.msgid.link/20260228221800.1082070-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>