LWIP_HOOK_TCP_ISN: added CHANGELOG/fixed comment

CHANGELOG

@@ -26,6 +26,10 @@ HISTORY
 
   ++ Bugfixes:
 
+  2016-12-15: David van Moolenbroek
+  * opt.h, tcp: added LWIP_HOOK_TCP_ISN() to implement less predictable initial
+    sequence numbers (see contrib/addons/tcp_isn for an example implementation)
+
   2016-12-05: Dirk Ziegelmeier
   * fixed compiling with IPv4 disabled (IPv6 only case)
   

src/include/lwip/opt.h

@@ -2415,8 +2415,8 @@
  * Hook for generation of the Initial Sequence Number (ISN) for a new TCP
  * connection. The default lwIP ISN generation algorithm is very basic and may
  * allow for TCP spoofing attacks. This hook provides the means to implement
- * the standardized ISN generation algorithm from RFC 6528, or any other
- * desired algorithm (e.g., it can be set to LWIP_RAND()), as a replacement.
+ * the standardized ISN generation algorithm from RFC 6528 (see contrib/adons/tcp_isn),
+ * or any other desired algorithm as a replacement.
  * Called from tcp_connect() and tcp_listen_input() when an ISN is needed for
  * a new TCP connection, if TCP support (@ref LWIP_TCP) is enabled.\n
  * Signature: u32_t my_hook_tcp_isn(const ip_addr_t* local_ip, u16_t local_port, const ip_addr_t* remote_ip, u16_t remote_port);