Allow an unpriviled user who has created a user namespace, and then
created a network namespace to effectively use the new network
namespace, by reducing capable(CAP_NET_ADMIN) calls to
ns_capable(net->user_ns,CAP_NET_ADMIN) calls.

Allow setting of the tun iff flags.
Allow creating of tun devices.
Allow adding a new queue to a tun device.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>