The value of tmnxMobPdnGaIfIndex specifies the interface
index of the local interface used for the Ga reference point.
When the value of this object is set to 0, no interface has
been assigned.
If tmnxMobPdnGaGtpPrimeGrpName is specified, then the value of
TIMETRA-MOBILE-PROFILE-MIB::tmnxMobGtpPriGrpIfIndex is used as the
interface index of the local interface used for the Ga reference
point.