We now only send enough data to fill other ends window, not past that.
Previous logic had a but that allowed sending too much data leading to
retransmissions.
When the target sends zero window and later updates window size,
immediately retransmit non-acknowledged bytes.
Don't validate packets through listeing socket twice. The actual socket
will already verify the checksum so the listening socket does not have
to.
Bananymous
ff378e4538