appletalk: use IS_ENABLED() instead of checking for built-in or module

The IS_ENABLED() macro checks if a Kconfig symbol has been enabled either
built-in or as a module, use that macro instead of open coding the same.

Using the macro makes the code more readable by helping abstract away some
of the Kconfig built-in and module enable details.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/appletalk/ddp.c

@@ -1278,7 +1278,7 @@ out:
 	return err;
 }
 
-#if defined(CONFIG_IPDDP) || defined(CONFIG_IPDDP_MODULE)
+#if IS_ENABLED(CONFIG_IPDDP)
 static __inline__ int is_ip_over_ddp(struct sk_buff *skb)
 {
 	return skb->data[12] == 22;