net: dsa: Add dsa_is_dsa_port() helper

Add an inline helper for determining is a port is a DSA port.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/dsa.h b/include/net/dsa.h
index bd9b765..b34d812 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -171,6 +171,11 @@
 	return !!(ds->index == ds->dst->cpu_switch && p == ds->dst->cpu_port);
 }
 
+static inline bool dsa_is_dsa_port(struct dsa_switch *ds, int p)
+{
+	return !!((ds->dsa_port_mask) & (1 << p));
+}
+
 static inline bool dsa_is_port_initialized(struct dsa_switch *ds, int p)
 {
 	return ds->phys_port_mask & (1 << p) && ds->ports[p];