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

drivers/net/ethernet/natsemi/ns83820.c

@@ -134,7 +134,7 @@ static int lnksts = 0;		/* CFG_LNKSTS bit polarity */
 
 /* tunables */
 #define RX_BUF_SIZE	1500	/* 8192 */
-#if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
+#if IS_ENABLED(CONFIG_VLAN_8021Q)
 #define NS83820_VLAN_ACCEL_SUPPORT
 #endif