ppp: Do not free not yet unregistered net device.

An error path in ppp_create_interface() lacks one and may
BUG in free_netdev() checking for proper dev->reg_state.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp_generic.c

@@ -2458,6 +2458,7 @@ ppp_create_interface(int unit, int *retp)
 
 out3:
 	atomic_dec(&ppp_unit_count);
+	unregister_netdev(dev);
 out2:
 	mutex_unlock(&all_ppp_mutex);
 	free_netdev(dev);