tcp: add tcp_tsopt_ecr_before helper

a helper to prepare the main RACK patch
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -2250,14 +2250,19 @@ static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
+static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
+{
+	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+	       before(tp->rx_opt.rcv_tsecr, when);
+}
+
 /* Nothing was retransmitted or returned timestamp is less
  * than timestamp of the first retransmission.
  */
 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
 {
 	return !tp->retrans_stamp ||
-		(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
-		 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
+	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
 }
 
 /* Undo procedures. */