atm_dev_deregister() removes device from atm_dev list immediately to
prevent operations on a phantom device.  Decision to free device based
only on ->refcnt  now. Remove shutdown_atm_dev() use atm_dev_deregister()
instead.  atm_dev_deregister() also asynchronously releases all vccs
related to device.
Signed-off-by: NStanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: NChas Williams <chas@cmf.nrl.navy.mil>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>