Classify untagged packets into a native vlan

In VCPE case, each bare metal server that is connected behind a port is
treated as a VM. Since we are modeling the interface as a vlan interface,
untagged packets should be marked as the property of a native vlan.

Add a new flag to the vif that will decide whether untagged packets should
be clasified to native vlan or not

Change-Id: I5d0f8cf3fc011a8ed74c0187974a088999be6531
Closes-BUG:#1387521