module: ietf-if-vlan-encapsulation

  augment /if:interfaces/if:interface/if-ext:encapsulation
            /if-ext:encaps-type:
    +--:(dot1q-vlan)
       +--rw dot1q-vlan
          +--rw outer-tag
          |  +--rw tag-type    dot1q-tag-type
          |  +--rw vlan-id     vlanid
          +--rw second-tag!
             +--rw tag-type    dot1q-tag-type
             +--rw vlan-id     vlanid