tcp: Call tcp_syn_ack_timeout() directly.

Since DCCP has been removed, we do not need to use
request_sock_ops.syn_ack_timeout().

Let's call tcp_syn_ack_timeout() directly.

Now other function pointers of request_sock_ops are
protocol-dependent.

Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/request_sock.h

···
 				      struct sk_buff *skb,
 				      enum sk_rst_reason reason);
 	void		(*destructor)(struct request_sock *req);
-	void		(*syn_ack_timeout)(const struct request_sock *req);
 };
 
 struct saved_syn {

net/ipv4/inet_connection_sock.c

···
 			young <<= 1;
 		}
 	}
+
 	syn_ack_recalc(req, max_syn_ack_retries, READ_ONCE(queue->rskq_defer_accept),
 		       &expire, &resend);
-	req->rsk_ops->syn_ack_timeout(req);
+	tcp_syn_ack_timeout(req);
+
 	if (!expire &&
 	    (!resend ||
 	     !tcp_rtx_synack(sk_listener, req) ||

net/ipv4/tcp_ipv4.c

···
 	.send_ack	=	tcp_v4_reqsk_send_ack,
 	.destructor	=	tcp_v4_reqsk_destructor,
 	.send_reset	=	tcp_v4_send_reset,
-	.syn_ack_timeout =	tcp_syn_ack_timeout,
 };
 
 const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {

net/ipv4/tcp_timer.c

···
 	struct tcp_sock *tp = tcp_sk(sk);
 	int max_retries;
 
-	req->rsk_ops->syn_ack_timeout(req);
+	tcp_syn_ack_timeout(req);
 
 	/* Add one more retry for fastopen.
 	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
···
 
 	__NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
 }
-EXPORT_IPV6_MOD(tcp_syn_ack_timeout);
 
 void tcp_reset_keepalive_timer(struct sock *sk, unsigned long len)
 {

net/ipv6/tcp_ipv6.c

···
 	.send_ack	=	tcp_v6_reqsk_send_ack,
 	.destructor	=	tcp_v6_reqsk_destructor,
 	.send_reset	=	tcp_v6_send_reset,
-	.syn_ack_timeout =	tcp_syn_ack_timeout,
 };
 
 const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {