net: loopback driver cleanup

loopback driver uses dev->ml_priv to store its percpu stats pointer.
It uses ugly casts "(void __percpu __force *)" to shut up sparse
complains.

Define an union to better document we use ml_priv in loopback driver and
define a lstats field with appropriate types.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 45dcda5b..01bd4c8 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1050,8 +1050,10 @@
 #endif
 
 	/* mid-layer private */
-	void			*ml_priv;
-
+	union {
+		void				*ml_priv;
+		struct pcpu_lstats __percpu	*lstats; /* loopback stats */
+	};
 	/* GARP */
 	struct garp_port	*garp_port;