The value of tmnxMobPdnApnChrgProfileRoaming specifies the charging
trigger rules applied for generating Charging Data Records (CDR) for
roaming subscribers.
If a corresponding charging profile does not exist in
TIMETRA-MOBILE-PROFILE-MIB::tmnxMobProfPgwChargingTable,
an 'inconsistentValue' error will be returned.
A value of '-1' specifies that charging profile information is
inherited from the value of tmnxMobPdnChargingProfRoaming which
specifies the charging trigger rules applied for roaming subscribers
at the gateway level.