The threshold value the route metric MUST reach in order for
the tracked object to transition to the 'down' state from the
'up' state.
This value MUST be greater than the value specified in
etsysTrackedObjectsRouteMetricUpThresh. An inconsistentValue
error is returned if the value of a set operation is less than
or equal to etsysTrackedObjectsRouteMetricUpThresh.
This value only has meaning when etsysTrackedObjectsRouteOption
is 'metric'.