net: make net_device members garp_port and mrp_port conditional

garp_port is only used in net/802/garp.c which is only compiled with
CONFIG_GARP enabled. Same goes for mrp_port which is only used in
net/802/mrp.c with CONFIG_MRP enabled.

Only include the two members in struct net_device if their respective
CONFIG_* is enabled. This saves a few bytes in struct net_device in case
CONFIG_GARP or CONFIG_MRP are not enabled.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1865,8 +1865,12 @@ struct net_device {
 		struct pcpu_vstats __percpu		*vstats;
 	};
 
+#if IS_ENABLED(CONFIG_GARP)
 	struct garp_port __rcu	*garp_port;
+#endif
+#if IS_ENABLED(CONFIG_MRP)
 	struct mrp_port __rcu	*mrp_port;
+#endif
 
 	struct device		dev;
 	const struct attribute_group *sysfs_groups[4];