tcp: tso: allow deferring under reordering state

While doing experiments with reordering resilience, we found
linux senders were not able to send at full speed under reordering,
because every incoming SACK was releasing one MSS.

This patch removes the limitation, as we did for CWR state
in commit a0ea700e ("tcp: tso: allow CA_CWR state in
tcp_tso_should_defer()")

Neal Cardwell had a concern about limited transmit so
Yuchung conducted experiments on GFE and found nothing
worth adding an extra check on fast path :

  if (icsk->icsk_ca_state == TCP_CA_Disorder &&
      tcp_sk(sk)->reordering == sysctl_tcp_reordering)
          goto send_now;
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -1774,7 +1774,7 @@ static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
 		goto send_now;
 
-	if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_CWR)))
+	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
 		goto send_now;
 
 	/* Avoid bursty behavior by allowing defer