Merge patch series "allow to create pidfds for reaped tasks with SCM_PIDFD"

This is a logical continuation of the earlier work to create pidfds for
reaped tasks through the SO_PEERPIDFD socket option merged in
923ea4d4482b ("Merge patch series "net, pidfs: enable handing out pidfds
for reaped sk->sk_peer_pid"").

* patches from https://lore.kernel.org/20250703222314.309967-1-aleksandr.mikhalitsyn@canonical.com:
  selftests: net: extend SCM_PIDFD test to cover stale pidfds
  af_unix: enable handing out pidfds for reaped tasks in SCM_PIDFD
  af_unix: stash pidfs dentry when needed
  af_unix/scm: fix whitespace errors
  af_unix: introduce and use scm_replace_pid() helper
  af_unix: introduce unix_skb_to_scm helper
  af_unix: rework unix_maybe_add_creds() to allow sleep

Link: https://lore.kernel.org/20250703222314.309967-1-aleksandr.mikhalitsyn@canonical.com
Signed-off-by: Christian Brauner <brauner@kernel.org>