[UM]: Fix use of skb after netif_rx

Recently, Wang Chen submitted a patch
(d30f53ae) to move a call to netif_rx(skb)
after a subsequent reference to skb, because netif_rx may call kfree_skb on
its argument.  The same problem occurs in some other drivers as well.

This was found using the following semantic match.
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
expression skb, e,e1;
@@

(
 netif_rx(skb);
|
 netif_rx_ni(skb);
)
  ... when != skb = e
(
  skb = e1
|
* skb
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/um/drivers/net_kern.c

@@ -98,10 +98,10 @@ static int uml_net_rx(struct net_device *dev)
 	if (pkt_len > 0) {
 		skb_trim(skb, pkt_len);
 		skb->protocol = (*lp->protocol)(skb);
-		netif_rx(skb);
 
 		lp->stats.rx_bytes += skb->len;
 		lp->stats.rx_packets++;
+		netif_rx(skb);
 		return pkt_len;
 	}