The current number of units of the resource in the system.
See the DESCRIPTION for juniSystemUtilizationResourceSubType for what
constitutes a unit of value for this object.
Note that some resource types may have instances that do not consume any
limited resources and therefore are not included in this count (e.g. IP
loopback interfaces do not consume routing resources and therefore don't
have a capacity limit, whereas 'external' IP interfaces do).