* ackhandler: check for missing packets below reordering treshold
No functional change expected.
With the Acknowledgement Frequency extension, the reordering threshold
will become configurable. With this change, it will be easy to use the
peer-requested value instead of the predefined constant.
* improve documentation
* call HighestMissingUpTo in randomized test
* ackhandler: use slice instead of linked list to track received packets
* ackhandler: add benchmark test for received packet history
* ackhandler: use the slices package for slice manipulations
Duplicate detection uses the same data structure that is used to track
received packets to generate ACK frames. That means that after an old
ACK range has been pruned, a severly delayed packet might be incorrectly
detected as a duplicate.
As we wouldn't have acknowledged receipt of this packet, this situation
would have resulted in a retransmission by the peer anyway, so dropping
the packet won't cause a big regression.
