UPSTREAM: net: add accept helper not installing fd

[ Upstream commit d32f89da ]

Introduce and reuse a helper that acts similarly to __sys_accept4_file()
but returns struct file instead of installing file descriptor. Will be
used by io_uring.

Change-Id: I27ff49709d0c3332ca9b831a62fecc14f7ef3304
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: David S. Miller <davem@davemloft.net>
Link: https://lore.kernel.org/r/c57b9e8e818d93683a3d24f8ca50ca038d1da8c4.1629888991.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ad0b0137)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>