The vRtrIfTmsOffRampVprn specifies the off-ramp VPRN service associated
with this threat-management service (TMS) interface.
An 'inconsistentValue' error is returned when this object is set to a
non-default value when vRtrIfType is not set to 'tmsService'.
An 'inconsistentValue' error is returned when this object is set to a
different value when vRtrIfRowStatus is set to 'active'.