netfilter: nf_conntrack: don't try to deliver events for untracked connections

The untracked conntrack actually does usually have events marked for
delivery as its not special-cased in that part of the code. Skip the
actual delivery since it impacts performance noticeably.
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netfilter/nf_conntrack_core.h

@@ -59,7 +59,7 @@ static inline int nf_conntrack_confirm(struct sk_buff *skb)
 	struct nf_conn *ct = (struct nf_conn *)skb->nfct;
 	int ret = NF_ACCEPT;
 
-	if (ct) {
+	if (ct && ct != &nf_conntrack_untracked) {
 		if (!nf_ct_is_confirmed(ct) && !nf_ct_is_dying(ct))
 			ret = __nf_conntrack_confirm(skb);
 		nf_ct_deliver_cached_events(ct);