[TCP]: Fixes IW > 2 cases when TCP is application limited

Whenever a transfer is application limited, we are allowed at least
initial window worth of data per window unless cwnd is previously
less than that.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -3541,7 +3541,8 @@ void tcp_cwnd_application_limited(struct sock *sk)
 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
 	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
 		/* Limited by application or receiver window. */
-		u32 win_used = max(tp->snd_cwnd_used, 2U);
+		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
+		u32 win_used = max(tp->snd_cwnd_used, init_win);
 		if (win_used < tp->snd_cwnd) {
 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
 			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;