Merge branch 'net-fix-inet_proto_csum_replace_by_diff-for-ipv6'

Paul Chaignon says:

====================
net: Fix inet_proto_csum_replace_by_diff for IPv6

This patchset fixes a bug that causes skb->csum to hold an incorrect
value when calling inet_proto_csum_replace_by_diff for an IPv6 packet
in CHECKSUM_COMPLETE state. This bug affects BPF helper
bpf_l4_csum_replace and IPv6 ILA in adj-transport mode.

In those cases, inet_proto_csum_replace_by_diff updates the L4 checksum
field after an IPv6 address change. These two changes cancel each other
in terms of checksum, so skb->csum shouldn't be updated.

v2: https://lore.kernel.org/aCz84JU60wd8etiT@mail.gmail.com
====================

Link: https://patch.msgid.link/cover.1748509484.git.paul.chaignon@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>