fix up stats_display which was added in previous commit

src/include/lwip/opt.h

@@ -356,6 +356,10 @@ a lot of data that needs to be copied, this should be set high. */
 
 #if LWIP_STATS
 
+#ifndef LWIP_STATS_DISPLAY
+#define LWIP_STATS_DISPLAY 0
+#endif
+
 #ifndef LINK_STATS
 #define LINK_STATS	1
 #endif

src/include/lwip/stats.h

@@ -144,6 +144,11 @@ void stats_init(void);
 #define LINK_STATS_INC(x)
 #endif
 
+/* Display of statistics */
+#if LWIP_STATS_DISPLAY
+void stats_display(void);
+#endif
+
 #endif /* __LWIP_STATS_H__ */