ipv6: 9.0 P2 backports from upstream

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2041401

v2: add followup update for commit 8837cbbf8542 ("net: ipv6: add fib6_nh_release_dsts stub"). Also add a optimize for the resilient nexthop group.

Signed-off-by: Hangbin Liu haliu@redhat.com