The maximum number of history buckets to record. When
the RttMonRttType is 'pathEcho' this value directly
represents a path to a target. For all other
RttMonRttTypes this value should be set to the number
of operations to keep per lifetime.
After rttMonHistoryAdminNumBuckets are filled, the
and the oldest entries are deleted and the most recent
rttMonHistoryAdminNumBuckets buckets are retained.