hamradio: 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>

drivers/net/hamradio/bpqether.c

@@ -484,7 +484,7 @@ static void bpq_setup(struct net_device *dev)
 	dev->flags      = 0;
 	dev->features	= NETIF_F_LLTX;	/* Allow recursion */
 
-#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
+#if IS_ENABLED(CONFIG_AX25)
 	dev->header_ops      = &ax25_header_ops;
 #endif