netfilter: fix compilation when conntrack is disabled but tproxy is enabled

The IPv6 tproxy patches split IPv6 defragmentation off of conntrack, but
failed to update the #ifdef stanzas guarding the defragmentation related
fields and code in skbuff and conntrack related code in nf_defrag_ipv6.c.

This patch adds the required #ifdefs so that IPv6 tproxy can truly be used
without connection tracking.

Original report:
http://marc.info/?l=linux-netdev&m=129010118516341&w=2

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: KOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 19d6c21..d31bb36 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -380,6 +380,8 @@
 	}
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
 	nf_conntrack_put(skb->nfct);
+#endif
+#ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
 	nf_conntrack_put_reasm(skb->nfct_reasm);
 #endif
 #ifdef CONFIG_BRIDGE_NETFILTER