Insert a service VLAN tag or customer VLAN tag into a packet.
A VLAN tag contains the VLAN ID field and the 802.1p priority
field. Both the service VLAN ID and the customer VLAN ID can
not be set at the same time. One of them must be set. The
802.1p priority of the service VLAN tag and that of the
customer VLAN tag can be set optionally. However, both of
them can not be set at the same time. The new setting
overwrites the previous one.