Current operational value for this variable. If the current
operational value cannot be reported:
- VariableOper will report 'N/A' if FeatureType is
string.
- VariableOper will be zero length otherwise.
If VariableOper reports not supported, but VariableCaps
reports non-zero length, this variable is write-only.
If FeatureType is string, a zero length VariableOper is
a valid value.