net: dsa: introduce the dsa_cpu_ports() helper

Similar to dsa_user_ports() which retrieves a port mask of all user
ports, introduce dsa_cpu_ports() which retrieves the mask of all CPU
ports of a switch.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/dsa.h

@@ -590,6 +590,17 @@ static inline u32 dsa_user_ports(struct dsa_switch *ds)
 	return mask;
 }
 
+static inline u32 dsa_cpu_ports(struct dsa_switch *ds)
+{
+	struct dsa_port *cpu_dp;
+	u32 mask = 0;
+
+	dsa_switch_for_each_cpu_port(cpu_dp, ds)
+		mask |= BIT(cpu_dp->index);
+
+	return mask;
+}
+
 /* Return the local port used to reach an arbitrary switch device */
 static inline unsigned int dsa_routing_port(struct dsa_switch *ds, int device)
 {