Use of vlan_index created problems unregistering vlans on guests.

In addition, tools delete vlan by tag, not by index, lets follow that.
Signed-off-by: NJack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>