[IPV6]: udp.c build fix

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index bb45b9b..efa8950 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -385,7 +385,7 @@
 	if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 		skb->csum = ~csum_unfold(csum_ipv6_magic(&skb->nh.ipv6h->saddr,
 							 &skb->nh.ipv6h->daddr,
-							 ulen, IPPROTO_UDP,
+							 skb->len, IPPROTO_UDP,
 							 0));
 
 	return (UDP_SKB_CB(skb)->partial_cov = 0);