[UDP]: Reread uh pointer after pskb_trim

The header may have moved when trimming.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

net/ipv4/udp.c

@@ -1137,6 +1137,7 @@ int udp_rcv(struct sk_buff *skb)
 
 	if (pskb_trim_rcsum(skb, ulen))
 		goto short_packet;
+	uh = skb->h.uh;
 
 	udp_checksum_init(skb, uh, ulen, saddr, daddr);