The listener interface for receiving SET validation events from MIB
browser. The class that is interested in processing events of this type
implements this interface, and the object created with that class is
registered with FTable object. The return value is an enum
ValueValidation. Application performs new value validation
and accepts it by returning ValueValidation.SUCCESS or rejects it by
returning any other ValueValidation.XXXX value.
The reject reason is sent to MIB browser.