commit f4e65870e5cede5ca1ec0006b6c9803994e5f7b8 upstream.

We need this functionality for the io_uring file registration, but
we cannot rely on it since CONFIG_UNIX can be modular. Move the helpers
to a separate file, that's always builtin to the kernel if CONFIG_UNIX is
m/y.

No functional changes in this patch, just moving code around.
Reviewed-by: NHannes Reinecke <hare@suse.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>