pppoe: drop PPPOX_ZOMBIEs in pppoe_release

When PPPOE is running over a virtual ethernet interface (e.g., a
bonding interface) and the user tries to delete the interface in case
the PPPOE state is ZOMBIE, the kernel will loop forever while
unregistering net_device for the reference count is not decreased to
zero which should have been done with dev_put().
Signed-off-by: Xiaodong Xu <stid.smth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp/pppoe.c

@@ -570,7 +570,7 @@ static int pppoe_release(struct socket *sock)
 
 	po = pppox_sk(sk);
 
-	if (sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND)) {
+	if (sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND | PPPOX_ZOMBIE)) {
 		dev_put(po->pppoe_dev);
 		po->pppoe_dev = NULL;
 	}