net: Make ax25_ptr depend on CONFIG_AX25

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ax25.h b/include/net/ax25.h
index 76fb39c..c91bc87 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -318,10 +318,12 @@ void ax25_digi_invert(const ax25_digi *, ax25_digi *);
 extern ax25_dev *ax25_dev_list;
 extern spinlock_t ax25_dev_lock;
 
+#if IS_ENABLED(CONFIG_AX25)
 static inline ax25_dev *ax25_dev_ax25dev(struct net_device *dev)
 {
 	return dev->ax25_ptr;
 }
+#endif
 
 ax25_dev *ax25_addr_ax25dev(ax25_address *);
 void ax25_dev_device_up(struct net_device *);