An index that uniquely identifies an entry in
the hostTopN table among those in the same report.
This index is between 1 and N, where N is the
number of entries in this table. Increasing values
of hostTopNIndex shall be assigned to entries with
decreasing values of hostTopNRate until index N
is assigned to the entry with the lowest value of
hostTopNRate or there are no more hostTopNEntries.