The value of tmnxL2tpLnsTuPppDefaultService specifies the
service ID of the service where the PPP sessions are established
when the authentication server does not specify the service ID.
The value zero specifies that that the actual value must be used
of the object tmnxL2tpLnsTgPppDefaultService.
If the value of tmnxL2tpLnsTuPppDefaultService is equal to zero, the
value of tmnxL2tpLnsTuPppDefaultGroupIf must also be equal to zero.