inet: drop prev pointer handling in request sock

When request sock are put in ehash table, the whole notion
of having a previous request to update dl_next is pointless.

Also, following patch will get rid of big purge timer,
so we want to delete a request sock without holding listener lock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index dd11ac7..848bcab 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -572,7 +572,6 @@
 
 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			   struct request_sock *req,
-			   struct request_sock **prev,
 			   bool fastopen)
 {
 	struct tcp_options_received tmp_opt;
@@ -766,7 +765,7 @@
 	if (child == NULL)
 		goto listen_overflow;
 
-	inet_csk_reqsk_queue_unlink(sk, req, prev);
+	inet_csk_reqsk_queue_unlink(sk, req);
 	inet_csk_reqsk_queue_removed(sk, req);
 
 	inet_csk_reqsk_queue_add(sk, req, child);
@@ -791,7 +790,7 @@
 		tcp_reset(sk);
 	}
 	if (!fastopen) {
-		inet_csk_reqsk_queue_drop(sk, req, prev);
+		inet_csk_reqsk_queue_drop(sk, req);
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
 	}
 	return NULL;