dev_change_netns on a tunnel device

[Sapan Bhatia]

Hi Eric,

Are the current semantics of tunnel devices (ipip, ip_gre etc.) with
respect to changing the current netns correct? These devices have an
ip_tunnel structure associated with each net_device, which is
currently a global (not per_net). The result is that you can set up in
container X a tunnel with endpoints associated with a device in
container Y in a different network namespace. This feature seems
useful, because you can hook up containers on 2 machines with one of
these tunnels, without using etun (or like) devices, but intuitively,
it seems that the tunnel module should be listening for a
DEV_UNREGISTER and reset it when the device is migrated

Sapan