If you rmmod a network device that is in a vlan, the system hangs waiting
for the refcount to go to zero, because it is -1.  The problem is that the
vlan notifier does an extra dev_put in NETDEV_UNREGISTER case of notifier.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@redhat.com>