tcp: add send_synack method to tcp_request_sock_ops

Create a new tcp_request_sock_ops method to unify the IPv4/IPv6
signature for tcp_v[46]_send_synack. This allows us to later unify
tcp_v4_rtx_synack with tcp_v6_rtx_synack and tcp_v4_conn_request with
tcp_v4_conn_request.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 4347826..b5945ac 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -814,6 +814,7 @@
  *	socket.
  */
 static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
+			      struct flowi *fl,
 			      struct request_sock *req,
 			      u16 queue_mapping,
 			      struct tcp_fastopen_cookie *foc)
@@ -846,7 +847,8 @@
 
 static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req)
 {
-	int res = tcp_v4_send_synack(sk, NULL, req, 0, NULL);
+	const struct  tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
+	int res = af_ops->send_synack(sk, NULL, NULL, req, 0, NULL);
 
 	if (!res) {
 		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
@@ -1285,6 +1287,7 @@
 #endif
 	.route_req	=	tcp_v4_route_req,
 	.init_seq	=	tcp_v4_init_sequence,
+	.send_synack	=	tcp_v4_send_synack,
 };
 
 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
@@ -1404,8 +1407,8 @@
 	tcp_openreq_init_rwin(req, sk, dst);
 	fastopen = !want_cookie &&
 		   tcp_try_fastopen(sk, skb, req, &foc, dst);
-	err = tcp_v4_send_synack(sk, dst, req,
-				 skb_get_queue_mapping(skb), &foc);
+	err = af_ops->send_synack(sk, dst, NULL, req,
+				  skb_get_queue_mapping(skb), &foc);
 	if (!fastopen) {
 		if (err || want_cookie)
 			goto drop_and_free;