Indicates the Ethernet protocol type of the outer VLAN tag of a port.
Options:
1. invalid(-1) -it indicates that the port does not support the
Ethernet protocol type of the outer VLAN. During the query,
the invalid value -1 is fixedly returned.
2. dot1qTpid(1) -it is valid for all service streams on the port.
3. dot1adTpid(2) -it is valid for only switching-oriented and
connection-oriented service streams with two VLAN tags on the port.
Default: dot1qTpid(1)