dev/xen/netfront:
In netif_free(), properly stop the interface and drain any pending
timers prior to disconnecting from the backend device.
Remove all media and detach our interface object from the system
prior to deleting it.
PR: kern/176471
Submitted by: Roger Pau Monne <roger.pau@citrix.com>
Reviewed by: gibbs
MFC after: 1 week