netfilter: xt_CT: fix crash while destroy ct templates

In (d871bef netfilter: ctnetlink: dump entries from the dying and
unconfirmed lists), we assume that all conntrack objects are
inserted in any of the existing lists. However, template conntrack
objects were not. This results in hitting BUG_ON in the
destroy_conntrack path while removing a rule that uses the CT target.

This patch fixes the situation by adding the template lists, which
is where template conntrack objects reside now.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
index a1d83cc..923cb20 100644
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -71,6 +71,7 @@
 	struct hlist_head	*expect_hash;
 	struct hlist_nulls_head	unconfirmed;
 	struct hlist_nulls_head	dying;
+	struct hlist_nulls_head tmpl;
 	struct ip_conntrack_stat __percpu *stat;
 	struct nf_ct_event_notifier __rcu *nf_conntrack_event_cb;
 	struct nf_exp_event_notifier __rcu *nf_expect_event_cb;