cxgb4: impose mandatory VLAN usage when non-zero TAG ID

When a non-zero VLAN Tag ID is passed to t4_set_vlan_acl()
then impose mandatory VLAN Usage with that VLAN ID.
I.e any other VLAN ID should result in packets getting
dropped.

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>