staging: octeon: 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>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/octeon/ethernet.c

@@ -248,7 +248,7 @@ static int cvm_oct_common_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct octeon_ethernet *priv = netdev_priv(dev);
 	int interface = INTERFACE(priv->port);
-#if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
+#if IS_ENABLED(CONFIG_VLAN_8021Q)
 	int vlan_bytes = 4;
 #else
 	int vlan_bytes = 0;