vlan: Move device unregistration before lower dev cleanup

Move the unregister_netdevice() call for the VLAN device before cleanup
for the lower device. This is needed by GVRP so it can send a leave
message before the applicant on the lower device is cleaned up.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>