RFC7323 recommends that if the timestamp option was negotiated
then all packets should carry a TCP Timestamp and any packets that
do not should be dropped.
Netstack implemented this behaviour. Linux OTOH does not and will
accept such packets. This change makes Netstack behaviour compatible
with Linux.
Also now that we allow such packets, we do need to update RTO calculations
based on these packets even if timestamp option is enabled.
PiperOrigin-RevId: 233432268
Change-Id: I9f4742ae6b63930ac3b5e37d8c238761e6a4b29f
efe5e737d7