ipv6: fix illegal mac_header comparison on 32bit

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv6/udp_offload.c

@@ -88,7 +88,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 
 		/* Check if there is enough headroom to insert fragment header. */
 		tnl_hlen = skb_tnl_header_len(skb);
-		if (skb->mac_header < (tnl_hlen + frag_hdr_sz)) {
+		if (skb_mac_header(skb) < skb->head + tnl_hlen + frag_hdr_sz) {
 			if (gso_pskb_expand_head(skb, tnl_hlen + frag_hdr_sz))
 				goto out;
 		}