af_unix: Explicitly include headers for non-pointer struct fields.

include/net/af_unix.h indirectly includes some definitions for structs.

Let's include such headers explicitly.

  linux/atomic.h   : scm_stat.nr_fds
  linux/net.h      : unix_sock.peer_wq
  linux/path.h     : unix_sock.path
  linux/spinlock.h : unix_sock.lock
  linux/wait.h     : unix_sock.peer_wake
  uapi/linux/un.h  : unix_address.name[]

linux/socket.h is removed as the structs there are not used directly,
and linux/un.h is clarified with uapi as un.h only exists under
include/uapi.

While at it, duplicate headers are removed from .c files.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250318034934.86708-4-kuniyu@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>