[TCP]: Fix left_out setting during FRTO

Without FRTO, the tcp_try_to_open is never called with
lost_out > 0 (see tcp_time_to_recover). However, when FRTO is
enabled, the !tp->lost condition is not used until end of FRTO
because that way TCP avoids premature entry to fast recovery
during FRTO.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -2037,7 +2037,7 @@ static void tcp_try_to_open(struct sock *sk, int flag)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	tp->left_out = tp->sacked_out;
+	tcp_sync_left_out(tp);
 
 	if (tp->retrans_out == 0)
 		tp->retrans_stamp = 0;