netdevice: Support DSA tagging when DSA is built as a module

This change corrects an error seen when DSA tagging is built as a module.
Without this change it is not possible to get XDSA tagged frames as the
test for tagging is stripped by the #ifdef check.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1789,7 +1789,7 @@ void dev_net_set(struct net_device *dev, struct net *net)
 
 static inline bool netdev_uses_dsa(struct net_device *dev)
 {
-#ifdef CONFIG_NET_DSA
+#if IS_ENABLED(CONFIG_NET_DSA)
 	if (dev->dsa_ptr != NULL)
 		return dsa_uses_tagged_protocol(dev->dsa_ptr);
 #endif