net: Make dn_ptr depend on CONFIG_DECNET

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 5eef6c8..d2ef35e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1800,7 +1800,9 @@ struct net_device {
 #endif
 	void 			*atalk_ptr;
 	struct in_device __rcu	*ip_ptr;
+#if IS_ENABLED(CONFIG_DECNET)
 	struct dn_dev __rcu     *dn_ptr;
+#endif
 	struct inet6_dev __rcu	*ip6_ptr;
 	void			*ax25_ptr;
 	struct wireless_dev	*ieee80211_ptr;