netfilter: conntrack: prefer tcp_error_log to pr_debug

pr_debug doesn't provide any information other than that a packet
did not match existing state but also was found to not create a new
connection.

Replaces this with tcp_error_log, which will also dump packets'
content so one can see if this is a stray FIN or RST.
Signed-off-by: Florian Westphal <fw@strlen.de>

net/netfilter/nf_conntrack_proto_tcp.c

@@ -835,7 +835,8 @@ static bool tcp_error(const struct tcphdr *th,
 
 static noinline bool tcp_new(struct nf_conn *ct, const struct sk_buff *skb,
 			     unsigned int dataoff,
-			     const struct tcphdr *th)
+			     const struct tcphdr *th,
+			     const struct nf_hook_state *state)
 {
 	enum tcp_conntrack new_state;
 	struct net *net = nf_ct_net(ct);
@@ -846,7 +847,7 @@ static noinline bool tcp_new(struct nf_conn *ct, const struct sk_buff *skb,
 
 	/* Invalid: delete conntrack */
 	if (new_state >= TCP_CONNTRACK_MAX) {
-		pr_debug("nf_ct_tcp: invalid new deleting.\n");
+		tcp_error_log(skb, state, "invalid new");
 		return false;
 	}
 
@@ -980,7 +981,7 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
 	if (tcp_error(th, skb, dataoff, state))
 		return -NF_ACCEPT;
 
-	if (!nf_ct_is_confirmed(ct) && !tcp_new(ct, skb, dataoff, th))
+	if (!nf_ct_is_confirmed(ct) && !tcp_new(ct, skb, dataoff, th, state))
 		return -NF_ACCEPT;
 
 	spin_lock_bh(&ct->lock);