Merge branch 'net-flow-dissector-allow-explicit-passing-of-netns'

Florian Westphal says:

====================
net: flow dissector: allow explicit passing of netns

Change since last version:
 fix kdoc comment warning reported by kbuild robot, no other changes,
 thus retaining RvB tags from Eric and Willem.
 v1: https://lore.kernel.org/netdev/20240607083205.3000-1-fw@strlen.de/

Years ago flow dissector gained ability to delegate flow dissection
to a bpf program, scoped per netns.

The netns is derived from skb->dev, and if that is not available, from
skb->sk.  If neither is set, we hit a (benign) WARN_ON_ONCE().

This WARN_ON_ONCE can be triggered from netfilter.
Known skb origins are nf_send_reset and ipv4 stack generated IGMP
messages.

Lets allow callers to pass the current netns explicitly and make
nf_tables use those instead.

This targets net-next instead of net because the WARN is benign and this
is not a regression.
====================

Link: https://lore.kernel.org/r/20240608221057.16070-1-fw@strlen.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>