l2tp: Fix L2TP_DEBUGFS ifdef tests.

We have to check CONFIG_L2TP_DEBUGFS_MODULE as well as
CONFIG_L2TP_DEBUGFS.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index a961c77..91b1b9c 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -133,7 +133,7 @@
 	void (*session_close)(struct l2tp_session *session);
 	void (*ref)(struct l2tp_session *session);
 	void (*deref)(struct l2tp_session *session);
-#ifdef CONFIG_L2TP_DEBUGFS
+#if defined(CONFIG_L2TP_DEBUGFS) || defined(CONFIG_L2TP_DEBUGFS_MODULE)
 	void (*show)(struct seq_file *m, void *priv);
 #endif
 	uint8_t			priv[0];	/* private data */