* ackhandler: simplify deletion of old packets in packet history
* ackhandler: use a slice to keep track of sent packets
This is a vastly simpler data structure than the combination of map
and linked list used before. It avoids using a linked list (bad cache
locality) and a sync.Pool (for list elements), as well as having to do
hash table lookups.
In the future, this can be easily replaces with a ring buffer, avoiding
all allocations.
* ackhandler: don't store packets that were declared lost
8f3a68b4eb