inet: makes syn_ack_timeout mandatory

There are two struct request_sock_ops providers, tcp and dccp.

inet_csk_reqsk_queue_prune() can avoid testing syn_ack_timeout being
NULL if we make it non NULL like syn_ack_timeout

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Cc: dccp@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index caf6e17..07f5579 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -574,6 +574,11 @@
 	kfree(inet_rsk(req)->opt);
 }
 
+void dccp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
+{
+}
+EXPORT_SYMBOL(dccp_syn_ack_timeout);
+
 static struct request_sock_ops dccp_request_sock_ops __read_mostly = {
 	.family		= PF_INET,
 	.obj_size	= sizeof(struct dccp_request_sock),
@@ -581,6 +586,7 @@
 	.send_ack	= dccp_reqsk_send_ack,
 	.destructor	= dccp_v4_reqsk_destructor,
 	.send_reset	= dccp_v4_ctl_send_reset,
+	.syn_ack_timeout = dccp_syn_ack_timeout,
 };
 
 int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)