i40e: disable local loopback on vmdq vsi

The local loopback should only be enabled for VSIs that are supporting
cascaded VEBs or VEPA setups.  This is not the case here, and we need
to stop the VEB from echoing the VMDQ VSI packets back at the VSI.

Change-ID: I9dfb6ac79db24d04360d7efde62d81e20abc5090
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>