drivers/net/xen-netfront.c: Use DIV_ROUND_UP

The kernel.h macro DIV_ROUND_UP performs the computation (((n) + (d) - 1) /
(d)) but is perhaps more readable.

An extract of the semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@haskernel@
@@

#include <linux/kernel.h>

@depends on haskernel@
expression n,d;
@@

(
- (n + d - 1) / d
+ DIV_ROUND_UP(n,d)
|
- (n + (d - 1)) / d
+ DIV_ROUND_UP(n,d)
)

@depends on haskernel@
expression n,d;
@@

- DIV_ROUND_UP((n),d)
+ DIV_ROUND_UP(n,d)

@depends on haskernel@
expression n,d;
@@

- DIV_ROUND_UP(n,(d))
+ DIV_ROUND_UP(n,d)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/net/xen-netfront.c

@@ -471,7 +471,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	unsigned int offset = offset_in_page(data);
 	unsigned int len = skb_headlen(skb);
 
-	frags += (offset + len + PAGE_SIZE - 1) / PAGE_SIZE;
+	frags += DIV_ROUND_UP(offset + len, PAGE_SIZE);
 	if (unlikely(frags > MAX_SKB_FRAGS + 1)) {
 		printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n",
 		       frags);