This probably make sense for TCP RTT/RTTVAR/CWND, but not
for TCP fastopen cookies.
Its better to try previous cookie. If it appears to be obsolete,
server will send us new cookie anyway.
Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>