[TCP] FRTO: Response should reset also snd_cwnd_cnt

Since purpose is to reduce CWND, we prevent immediate growth. This
is not a major issue nor is "the correct way" specified anywhere.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -2490,6 +2490,7 @@ static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
 {
 	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+	tp->snd_cwnd_cnt = 0;
 	tcp_moderate_cwnd(tp);
 }