[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/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index b189278..c0e0fa0 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -463,7 +463,7 @@
 			if (time_after_eq(now, req->expires)) {
 				if ((req->retrans < thresh ||
 				     (inet_rsk(req)->acked && req->retrans < max_retries))
-				    && !req->rsk_ops->rtx_syn_ack(parent, req, NULL)) {
+				    && !req->rsk_ops->rtx_syn_ack(parent, req)) {
 					unsigned long timeo;
 
 					if (req->retrans++ == 0)