Merge branch 'netlink-fix-a-dump-livelock-with-a-notification-queued'

Jhonata Poma-Hansen says:

====================
netlink: fix a dump livelock with a notification queued

A netlink dump that starts while a notification is still charged to a
socket with a small receive buffer fails with ENOBUFS, and every retry
from recvmsg() fails the same way. A reader that peeks before reading,
as libnl does, never consumes the message at the head of the queue and
spins forever. I hit this with "iw dev wlan0 scan" on an arm64 board.

Patch 1 goes back to checking sk_rcvbuf before charging the dump skb,
as before commit ae8f160e7eb2. Patch 2 adds a selftest; it fails
without patch 1 and is skipped without the privileges to create a
netns.
====================

Link: https://patch.msgid.link/20261027-netlink-dump-livelock-v2-0-c4bb05352a33@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>