The sampling interval in seconds during which
statistics are collected for this report.
When this is set a value and the corresponding
portTopNControlEntry is valid, the
portTopNTimeRemaining object shall be set to the
same value.
portTopNTimeRemaining starts at the same value as
portTopNDuration and counts down as the collection
goes on.
If this object is set to be zero, it will do the
collection immediately. And the collecting report
value should be the absolute counter value.