The value of tmnxMobPdnS5GtpcIfIndex specifies the interface
index of the local interface used for the General Packet Radio
Services Tunneling Protocol for Control Plane (GTP-C) signaling.
When the value of this object is set to 0, no interface has
been assigned.
If value of this object is not set then the value of
tmnxMobServSigDefaultIfIndex is used.