netfilter: use consistent ipv4 network offset in xt_AUDIT

Even though the skb->data pointer has been moved from the link layer
header to the network layer header, use the same method to calculate the
offset in ipv4 and ipv6 routines.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: munged subject line]
Signed-off-by: Paul Moore <paul@paul-moore.com>

net/netfilter/xt_AUDIT.c

@@ -76,7 +76,7 @@ static void audit_ip4(struct audit_buffer *ab, struct sk_buff *skb)
 	struct iphdr _iph;
 	const struct iphdr *ih;
 
-	ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
+	ih = skb_header_pointer(skb, skb_network_offset(skb), sizeof(_iph), &_iph);
 	if (!ih) {
 		audit_log_format(ab, " truncated=1");
 		return;