net: Allow the userns root to control vlans.

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) and
capable(CAP_NET_RAW) calls to be ns_capable(net->user_ns,
CAP_NET_ADMIN), or capable(net->user_ns, CAP_NET_RAW) calls.

Allow the vlan ioctls:
SET_VLAN_INGRESS_PRIORITY_CMD
SET_VLAN_EGRESS_PRIORITY_CMD
SET_VLAN_FLAG_CMD
SET_VLAN_NAME_TYPE_CMD
ADD_VLAN_CMD
DEL_VLAN_CMD

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>