[UM]: Fix use of skb after netif_rx

Recently, Wang Chen submitted a patch
(d30f53aeb31d453a5230f526bea592af07944564) 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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

arch/um/drivers/net_kern.c

···
 	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;
 	}