tcp: move icsk_rto init to tcp_disconnect()

If we make sure a listener always has its icsk_rto
field set to TCP_TIMEOUT_INIT, we do not need to rewrite
this field after a new clone is created.

tcp_disconnect() is very seldom used in real applications.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2579,6 +2579,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	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_cnt = 0;
 	tp->window_clamp = 0;

net/ipv4/tcp_minisocks.c

@@ -482,7 +482,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 	newtp->srtt_us = 0;
 	newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
 	minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
-	newicsk->icsk_rto = TCP_TIMEOUT_INIT;
 	newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
 
 	newtp->packets_out = 0;