Vlan VPN TPID mode.
The value 'port-based' means VLAN VPN TPID value would be set based
on port via hh3cifVlanVPNTPID. In this situation, hh3cVlanVPNTPID is
meaningless and always return 0x8100.
The value 'global' means VLAN VPN TPID value should be set globally
via hh3cVlanVPNTPID. In this situation, hh3cifVlanVPNTPID in hh3cethernetTable
has the same value with hh3cVlanVPNTPID.