Merge branch 'ipv6-fix-ecmp-route-failover-on-carrier-loss'

Merge branch 'ipv6-fix-ecmp-route-failover-on-carrier-loss'

Sagarika Sharma says:

====================
ipv6: fix ECMP route failover on carrier loss

This patchset resolves an issue where established IPv6 connections are
unable to transition to alternative ECMP nexthops upon carrier loss.

Unlike IPv4, the IPv6 routing subsystem does not actively invalidate
cached destinations during a NETDEV_CHANGE event. Sockets persist
with dead routes, leading to stalled traffic or connection drops.

This series introduces a fix to trigger route invalidation by
updating the route serial number on link carrier loss and provides
a corresponding selftest to validate the failover behavior for IPv4
and IPv6.
====================

Link: https://patch.msgid.link/20260430200909.527827-1-sharmasagarika@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>