netfilter: nf_defrag: move NF_CONNTRACK bits into #ifdef

We cannot access the skb->_nfct field when CONFIG_NF_CONNTRACK is
disabled:

net/ipv4/netfilter/nf_defrag_ipv4.c: In function 'ipv4_conntrack_defrag':
net/ipv4/netfilter/nf_defrag_ipv4.c:83:9: error: 'struct sk_buff' has no member named '_nfct'
net/ipv6/netfilter/nf_defrag_ipv6_hooks.c: In function 'ipv6_defrag':
net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68:9: error: 'struct sk_buff' has no member named '_nfct'

Both functions already have an #ifdef for this, so let's move the
check in there.

Fixes: 902d6a4c ("netfilter: nf_defrag: Skip defrag if NOTRACK is set")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nf_defrag_ipv4.c

@@ -78,9 +78,11 @@ static unsigned int ipv4_conntrack_defrag(void *priv,
 	if (skb_nfct(skb) && !nf_ct_is_template((struct nf_conn *)skb_nfct(skb)))
 		return NF_ACCEPT;
 #endif
+	if (skb->_nfct == IP_CT_UNTRACKED)
+		return NF_ACCEPT;
 #endif
 	/* Gather fragments. */
-	if (skb->_nfct != IP_CT_UNTRACKED && ip_is_fragment(ip_hdr(skb))) {
+	if (ip_is_fragment(ip_hdr(skb))) {
 		enum ip_defrag_users user =
 			nf_ct_defrag_user(state->hook, skb);
 

net/ipv6/netfilter/nf_defrag_ipv6_hooks.c

@@ -63,10 +63,10 @@ static unsigned int ipv6_defrag(void *priv,
 	/* Previously seen (loopback)?	*/
 	if (skb_nfct(skb) && !nf_ct_is_template((struct nf_conn *)skb_nfct(skb)))
 		return NF_ACCEPT;
-#endif
 
 	if (skb->_nfct == IP_CT_UNTRACKED)
 		return NF_ACCEPT;
+#endif
 
 	err = nf_ct_frag6_gather(state->net, skb,
 				 nf_ct6_defrag_user(state->hook, skb));