[IPV4] udp: trim forgets about CHECKSUM_HW

A UDP packet may contain extra data that needs to be trimmed off.
But when doing so, UDP forgets to fixup the skb checksum if CHECKSUM_HW
is being used.

I think this explains the case of a NFS receive using skge driver
causing 'udp hw checksum failures' when interacting with a crufty
settop box.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -1141,7 +1141,7 @@ int udp_rcv(struct sk_buff *skb)
 	if (ulen > len || ulen < sizeof(*uh))
 		goto short_packet;
 
-	if (pskb_trim(skb, ulen))
+	if (pskb_trim_rcsum(skb, ulen))
 		goto short_packet;
 
 	if (udp_checksum_init(skb, uh, ulen, saddr, daddr) < 0)