Minor: Documentation update

doc/rawapi.txt

@@ -458,6 +458,9 @@ assembly or inline replacements for htons() and htonl()
 if you're using a little-endian architecture.
 #define lwip_htons(x) <your_htons>
 #define lwip_htonl(x) <your_htonl>
+If you #define them to htons() and htonl(), you should
+#define LWIP_DONT_PROVIDE_BYTEORDER_FUNCTIONS to prevent lwIP from
+defining hton*/ntoh* compatibility macros.
 
 Check your network interface driver if it reads at
 a higher speed than the maximum wire-speed. If the