The value of tmnxL2tpLnsTuPppLcpKaHoldUp specifies
how many LCP keepalive messages can be missed before the related
session is brought down.
The value zero specifies that the actual value must be used
of the object tmnxL2tpLnsTgPppLcpKaHoldUp.
If the value of tmnxL2tpLnsTuPppLcpKaHoldUp is equal to zero, the
value of tmnxL2tpLnsTuPppLcpKaInterval must also be equal to zero.