tcp: move snd_cwnd & snd_cwnd_cnt init to tcp_disconnect()

Passive connections can inherit proper value by cloning,
if we make sure all listeners have the proper values there.

tcp_disconnect() was setting snd_cwnd to 2, which seems
quite obsolete since IW10 adoption.

Also remove an obsolete comment.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2578,10 +2578,10 @@ int tcp_disconnect(struct sock *sk, int flags)
 	if (tp->write_seq == 0)
 		tp->write_seq = 1;
 	icsk->icsk_backoff = 0;
-	tp->snd_cwnd = 2;
 	icsk->icsk_probes_out = 0;
 	icsk->icsk_rto = TCP_TIMEOUT_INIT;
 	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+	tp->snd_cwnd = TCP_INIT_CWND;
 	tp->snd_cwnd_cnt = 0;
 	tp->window_clamp = 0;
 	tp->delivered_ce = 0;

net/ipv4/tcp_minisocks.c

@@ -490,14 +490,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 	newtp->last_oow_ack_time = 0;
 	newtp->total_retrans = req->num_retrans;
 
-	/* So many TCP implementations out there (incorrectly) count the
-	 * initial SYN frame in their delayed-ACK and congestion control
-	 * algorithms that we must have the following bandaid to talk
-	 * efficiently to them.  -DaveM
-	 */
-	newtp->snd_cwnd = TCP_INIT_CWND;
-	newtp->snd_cwnd_cnt = 0;
-
 	/* There's a bubble in the pipe until at least the first ACK. */
 	newtp->app_limited = ~0U;