Vlan VPN TPID mode.
The value 'port-based' means VLAN VPN TPID value would be set based
on port via hpnicfifVlanVPNTPID. In this situation, hpnicfVlanVPNTPID is
meaningless and always return 0x8100.
The value 'global' means VLAN VPN TPID value should be set globally
via hpnicfVlanVPNTPID. In this situation, hpnicfifVlanVPNTPID in hpnicfethernetTable
has the same value with hpnicfVlanVPNTPID.