If there is a Timestamps option in the arriving segment and SEG.TSval
< TS.Recent and if TS.Recent is valid, then treat the arriving segment
as not acceptable: Send an acknowledgement in reply as specified in
RFC-793 page 69 and drop the segment.
https://tools.ietf.org/html/rfc1323#page-19
PiperOrigin-RevId: 312590678
Zeling Feng