Merge branch 'af_unix-random-improvements-for-gc'

Kuniyuki Iwashima says:

====================
af_unix: Random improvements for GC.

If more than 16000 inflight AF_UNIX sockets exist on a host, each
sendmsg() will be forced to wait for unix_gc() even if a process
is not sending any FD.

This series tries not to impose such a penalty on sane users who
do not send AF_UNIX FDs or do not have inflight sockets more than
SCM_MAX_FD * 8.

The first patch can be backported to -stable.

Cleanup patches for commit 69db702c8387 ("io_uring/af_unix: disable
sending io_uring over sockets") and large refactoring of GC will
be followed later.

v4: https://lore.kernel.org/netdev/20231219030102.27509-1-kuniyu@amazon.com/
v3: https://lore.kernel.org/netdev/20231218075020.60826-1-kuniyu@amazon.com/
v2: https://lore.kernel.org/netdev/20231123014747.66063-1-kuniyu@amazon.com/
v1: https://lore.kernel.org/netdev/20231122013629.28554-1-kuniyu@amazon.com/
====================

Link: https://lore.kernel.org/r/20240123170856.41348-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>