Minor: Documentation update

src/core/def.c

@@ -11,6 +11,10 @@
  * \#define lwip_htonl(x) your_htonl
  *
  * Note lwip_ntohs() and lwip_ntohl() are merely references to the htonx counterparts.
+ * 
+ * If you #define them to htons() and htonl(), you should
+ * \#define LWIP_DONT_PROVIDE_BYTEORDER_FUNCTIONS to prevent lwIP from
+ * defining htonx/ntohx compatibility macros.
  */
 
 /*