[openib-general] netdev reference counting problem with ib_at

[Roland Dreier]

If I configure an IPoIB interface, load the ib_at module, and then try
to remove the ib_ipoib module, the module removal gets stuck with an
endless stream of

    unregister_netdevice: waiting for ib0 to become free. Usage count = 1

This is really bad, because as far as I can tell, there's no way to
recover from this situation other than rebooting.

ib_at needs to be reworked so that it doesn't keep perpetual
references to netdevs.

 - R.