From: Andrei Vagin <redacted>
Date: Mon, 24 Oct 2016 18:29:13 -0700

From: Andrey Vagin <redacted>

Each socket operates in a network namespace where it has been created,
so if we want to dump and restore a socket, we have to know its network
namespace.

We have a socket_diag to get information about sockets, it doesn't
report sockets which are not bound or connected.

This patch introduces a new socket ioctl, which is called SIOCGSKNS
and used to get a file descriptor for a socket network namespace.

A task must have CAP_NET_ADMIN in a target network namespace to
use this ioctl.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric W. Biederman <redacted>
Signed-off-by: Andrei Vagin <redacted>

Applied.