atm: [br2684] Fix oops due to skb->dev being NULL

It happens that if a packet arrives in a VC between the call to open it on
the hardware and the call to change the backend to br2684, br2684_regvcc
processes the packet and oopses dereferencing skb->dev because it is
NULL before the call to br2684_push().
Signed-off-by: NJorge Boncompte [DTI2] <jorge@dti2.net>
Signed-off-by: NChas Williams <chas@cmf.nrl.navy.mil>

net/atm/br2684.c

@@ -518,9 +518,9 @@ static int br2684_regvcc(struct atm_vcc *atmvcc, void __user * arg)
 		struct sk_buff *next = skb->next;
 
 		skb->next = skb->prev = NULL;
+		br2684_push(atmvcc, skb);
 		BRPRIV(skb->dev)->stats.rx_bytes -= skb->len;
 		BRPRIV(skb->dev)->stats.rx_packets--;
-		br2684_push(atmvcc, skb);
 
 		skb = next;
 	}