[NETFILTER]: ip_nat_snmp call skb_make_writable()

The snmp helper needs an explicit call to skb_ip_make_writable.
Please apply.
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@redhat.com>

net/ipv4/netfilter/ip_nat_snmp_basic.c

@@ -1252,6 +1252,9 @@ static unsigned int nat_help(struct ip_conntrack *ct,
 	int dir = CTINFO2DIR(ctinfo);
 	struct iphdr *iph = (*pskb)->nh.iph;
 	struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
+	
+	if (!skb_ip_make_writable(pskb, (*pskb)->len))
+		return NF_DROP;
 
 	spin_lock_bh(&snmp_lock);