This object selects the acctngFileTable entry for the collection
statistics for this interface type. The value of this object is the
same as the acctngFileIndex and is used to cross reference accounting
data files in the AcctngFileTable.
If the value of this object is zero (special value), then the combined
interface type/location defined by this entry is collected into all
entries in the acctngFileTable, i.e., all accounting files.