Neither OpenVZ or XEN containers can do anything with the tunnel info,
since tunnels are created in the root context and all the container
sees is an interface. We have a hack in the client side for openvz,
but rather then try to duplicate that hack for every XEN guest, lets
do this the right way, and return plain ifconfig lines from tmcd and
config them like any other interface. Since we rely on MAC addresses
to do this, we now return MACs to the root context when it gets the
tunnel info.

To do this we need to know the difference between the root context
asking for info *about* the container, and the container asking for
its *own* info. Since both XEN and OpenVZ containers are redirected
through the tmcc proxy, I changed the protocol so tmcd can tell who is
asking. This is imperfect, since we might someday want the container
to bypass the proxy, but for now it will do.

The other consideration is that a XEN container might have requested a
public IP, in which case it could actually do all of the tunnel stuff
itself, but then again we have to worry about all of the guests being
able to do tunnels, and so the easiest thing to do is just always do
it in the root context for the container.