[PPP] pppoe: Fix skb_unshare_check call position

The skb_unshare_check call needs to be made before pskb_may_pull,
not after.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/pppoe.c

@@ -385,12 +385,12 @@ static int pppoe_rcv(struct sk_buff *skb,
 	struct pppoe_hdr *ph;
 	struct pppox_sock *po;
 
-	if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
-		goto drop;
-
 	if (!(skb = skb_share_check(skb, GFP_ATOMIC)))
 		goto out;
 
+	if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
+		goto drop;
+
 	ph = pppoe_hdr(skb);
 
 	po = get_item((unsigned long) ph->sid, eth_hdr(skb)->h_source, dev->ifindex);