Use estimated RTT for receive buffer auto resizing instead of timestamps
Switched from using timestamps to RTT estimates when performing TCP receive
buffer auto resizing, as not all hosts support / enable TCP timestamps.
Disabled reset of receive buffer auto scaling when not in bulk receive mode,
which gives an extra 20% performance increase.
Also extracted auto resizing to a common method shared between standard and
With this AWS S3 downloads at ~17ms latency on a 1Gbps connection jump from
~3MB/s to ~100MB/s using the default settings.
Reviewed by: lstewart, gnn
MFC after: 2 weeks
Sponsored by: Multiplay
Differential Revision: https://reviews.freebsd.org/D9668