[PATCH] multicast broken on x86_64

The x86-64 implementation of csum-partial.c causes it to compute the
checksum incorrectly.

As a result, multicast doesn't work.  It looks as though iptables is
also affected.

Here's a simple patch.

arch/x86_64/lib/csum-partial.c

@@ -145,6 +145,6 @@ EXPORT_SYMBOL(csum_partial);
  */
 unsigned short ip_compute_csum(unsigned char * buff, int len)
 {
-	return ~csum_partial(buff,len,0); 
+	return csum_fold(csum_partial(buff,len,0));
 }