Merge branch 'af_unix-fix-a-null-deref-in-sk_diag_dump_uid'

Kuniyuki Iwashima says:

====================
af_unix: Fix a NULL deref in sk_diag_dump_uid().

The first patch fixes a NULL deref when we dump a AF_UNIX socket's UID,
and the second patch adds a repro/test for such a case.
====================

Link: https://lore.kernel.org/r/20221127012412.37969-1-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>