fixup: update documentation about he_pmtud_state_change_cb_t

include/he.h

@@ -528,7 +528,14 @@ typedef he_return_code_t (*he_pmtud_time_cb_t)(he_conn_t *conn, int timeout, voi
  * @param context A pointer to the user defined context
  * @see he_conn_set_context Sets the value of the context pointer
  *
- * Whenever Lightway PMTUD changes state, this function will be called.
+ * Whenever Lightway PMTUD changes state, this function will be called. This callback is
+ * mostly for informational only, there's no hard expectation for the callback to do anything.
+ * However, this callback may be useful for certain application logic which is triggered by the
+ * state changes.
+ *
+ * The host application must register this callback to enable Path MTU discovery.
+ *
+ * @see RFC 8899 for more information about PMTUD state machines.
  */
 typedef he_return_code_t (*he_pmtud_state_change_cb_t)(he_conn_t *conn, he_pmtud_state_t state,
                                                        void *context);

public/he.h

@@ -528,7 +528,14 @@ typedef he_return_code_t (*he_pmtud_time_cb_t)(he_conn_t *conn, int timeout, voi
  * @param context A pointer to the user defined context
  * @see he_conn_set_context Sets the value of the context pointer
  *
- * Whenever Lightway PMTUD changes state, this function will be called.
+ * Whenever Lightway PMTUD changes state, this function will be called. This callback is
+ * mostly for informational only, there's no hard expectation for the callback to do anything.
+ * However, this callback may be useful for certain application logic which is triggered by the
+ * state changes.
+ *
+ * The host application must register this callback to enable Path MTU discovery.
+ *
+ * @see RFC 8899 for more information about PMTUD state machines.
  */
 typedef he_return_code_t (*he_pmtud_state_change_cb_t)(he_conn_t *conn, he_pmtud_state_t state,
                                                        void *context);
@@ -1047,7 +1054,7 @@ void he_ssl_ctx_set_populate_network_config_ipv4_cb(
     he_ssl_ctx_t *ctx, he_populate_network_config_ipv4_cb_t pop_network_cb);
 
 /**
- * @brief Sets the function that will be called when Lightway PMTUD changes state
+ * @brief Sets the function that will be called when Lightway PMTUD changes state.
  * @param ctx A pointer to a valid SSL context
  * @param pmtud_state_change_cb The function to be called when Lightway PMTUD changes state
  * @note This callback function is optional if the implementation never intends to use the PMTUD

src/he/ssl_ctx.h

@@ -471,7 +471,7 @@ void he_ssl_ctx_set_populate_network_config_ipv4_cb(
     he_ssl_ctx_t *ctx, he_populate_network_config_ipv4_cb_t pop_network_cb);
 
 /**
- * @brief Sets the function that will be called when Lightway PMTUD changes state
+ * @brief Sets the function that will be called when Lightway PMTUD changes state.
  * @param ctx A pointer to a valid SSL context
  * @param pmtud_state_change_cb The function to be called when Lightway PMTUD changes state
  * @note This callback function is optional if the implementation never intends to use the PMTUD