netfilter: Use nf_ct_net instead of dev_net(out) in nf_nat_masquerade_ipv6

Use nf_ct_net(ct) instead of guessing that the netdevice out can
reliably report the network namespace the conntrack operation is
happening in.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv6/netfilter/nf_nat_masquerade_ipv6.c

@@ -34,7 +34,7 @@ nf_nat_masquerade_ipv6(struct sk_buff *skb, const struct nf_nat_range *range,
 	NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
 			    ctinfo == IP_CT_RELATED_REPLY));
 
-	if (ipv6_dev_get_saddr(dev_net(out), out,
+	if (ipv6_dev_get_saddr(nf_ct_net(ct), out,
 			       &ipv6_hdr(skb)->daddr, 0, &src) < 0)
 		return NF_DROP;