Description: af_unix: fix races in sk_peer_pid and sk_peer_cred accesses
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=2036934
 https://lore.kernel.org/netdev/20210929225750.2548112-1-eric.dumazet@gmail.com/T/
 https://bugs.chromium.org/p/project-zero/issues/detail?id=2230
Notes:
 carnil> Commit fixes 109f6e39fa07 ("af_unix: Allow SO_PEERCRED to work
 carnil> across namespaces.").
Bugs:
upstream: released (5.15-rc4) [35306eb23814444bd4021f8a1c3047d3cb0c8b2b]
5.10-upstream-stable: released (5.10.71) [3db53827a0e9130d9e2cbe3c3b5bca601caa4c74]
4.19-upstream-stable: released (4.19.209) [0512a9aede6e4417c4fa6e0042a7ca8bc7e06b86]
4.9-upstream-stable: released (4.9.286) [09818f629bafbe20e24bac919019853ea3ac5ca4]
sid: released (5.14.12-1)
5.10-bullseye-security: released (5.10.84-1)
4.19-buster-security: released (4.19.232-1)
4.9-stretch-security: released (4.9.290-1)