[INET]: Remove struct dst_entry *dst from request_sock_ops.rtx_syn_ack.

It looks like dst parameter is used in this API due to historical
reasons.  Actually, it is really used in the direct call to
tcp_v4_send_synack only.  So, create a wrapper for tcp_v4_send_synack
and remove dst from rtx_syn_ack.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 256032a..3b26f95 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -723,8 +723,8 @@
  *	This still operates on a request_sock only, not on a big
  *	socket.
  */
-static int tcp_v4_send_synack(struct sock *sk, struct request_sock *req,
-			      struct dst_entry *dst)
+static int __tcp_v4_send_synack(struct sock *sk, struct request_sock *req,
+				struct dst_entry *dst)
 {
 	const struct inet_request_sock *ireq = inet_rsk(req);
 	int err = -1;
@@ -732,7 +732,7 @@
 
 	/* First, grab a route. */
 	if (!dst && (dst = inet_csk_route_req(sk, req)) == NULL)
-		goto out;
+		return -1;
 
 	skb = tcp_make_synack(sk, dst, req);
 
@@ -751,11 +751,15 @@
 		err = net_xmit_eval(err);
 	}
 
-out:
 	dst_release(dst);
 	return err;
 }
 
+static int tcp_v4_send_synack(struct sock *sk, struct request_sock *req)
+{
+	return __tcp_v4_send_synack(sk, req, NULL);
+}
+
 /*
  *	IPv4 request_sock destructor.
  */
@@ -1380,7 +1384,7 @@
 	}
 	tcp_rsk(req)->snt_isn = isn;
 
-	if (tcp_v4_send_synack(sk, req, dst))
+	if (__tcp_v4_send_synack(sk, req, dst))
 		goto drop_and_free;
 
 	if (want_cookie) {