net: dsa: split dsa_port's netdev member

The dsa_port structure has a "netdev" member, which can be used for
either the master device, or the slave device, depending on its type.

It is true that today, CPU port are not exposed to userspace, thus the
port's netdev member can be used to point to its master interface.

But it is still slightly confusing, so split it into more explicit
"master" and "slave" members inside an anonymous union.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/dsa.h b/include/net/dsa.h
index 2746741..6ed1a17 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -164,6 +164,14 @@ struct dsa_mall_tc_entry {
 
 
 struct dsa_port {
+	/* A CPU port is physically connected to a master device.
+	 * A user port exposed to userspace has a slave device.
+	 */
+	union {
+		struct net_device *master;
+		struct net_device *slave;
+	};
+
 	/* CPU port tagging operations used by master or slave devices */
 	const struct dsa_device_ops *tag_ops;
 
@@ -176,7 +184,6 @@ struct dsa_port {
 	unsigned int		index;
 	const char		*name;
 	struct dsa_port		*cpu_dp;
-	struct net_device	*netdev;
 	struct device_node	*dn;
 	unsigned int		ageing_time;
 	u8			stp_state;