Number of out-of-order datagrams received.

- n (Int32)
- Statistics set index

Number of datagrams received out of order.

A datagram is counted as out of order if it fills a previously detected
sequence gap, but is not a retransmission. Note that if the duplicates counter
duplicate_data, above) increases along with this statistic, this implies the
arrivals of retransmitted datagrams before their originals.
This method returns a value from the nth set of statistics
encapsulated within this object.