ipv6: add a new namespace for nf_conntrack_reasm

As pointed by Michal, it is necessary to add a new
namespace for nf_conntrack_reasm code, this prepares
for the second patch.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Michal Kubeček <mkubecek@suse.cz>
Cc: David Miller <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 0318104..214cb0a 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -71,4 +71,12 @@
 #endif
 #endif
 };
+
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+struct netns_nf_frag {
+	struct netns_sysctl_ipv6 sysctl;
+	struct netns_frags	frags;
+};
+#endif
+
 #endif