vlan: unlink the upper neighbour before unregistering

On netdev unregister we're removing also all of its sysfs-associated stuff,
including the sysfs symlinks that are controlled by netdev neighbour code.
Also, it's a subtle race condition - cause we can still access it after
unregistering.

Move the unlinking right before the unregistering to fix both.

CC: Patrick McHardy <kaber@trash.net>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>