- Always split segments larger than MSS.
Currently, we base the segment split decision as a function of the
send congestion window and MSS, which could be greater than the MSS
advertised by remote.
- While splitting segments, ensure the PSH flag is reset when there
are segments that are queued to be sent.
- With TCP_CORK, hold up segments up until MSS. Fix a bug in computing
available send space before attempting to coalesce segments.
Fixes#2832
PiperOrigin-RevId: 314802928