Don't allow frame submission for pending new frame

This is partial revert of bbe4f5a3.
Only documentation is reverted.  Since we have 2 queues to handle
maximum concurrent streams, we are not ready to allow immediate frame
submission for pending new frames.

lib/includes/nghttp2/nghttp2.h

@@ -2239,13 +2239,11 @@ int nghttp2_priority_spec_check_default(const nghttp2_priority_spec *pri_spec);
  *
  * .. warning::
  *
- *   This function returns assigned stream ID if it succeeds and
- *   |stream_id| is -1.  But that stream is not opened yet.  The
- *   application must not submit WINDOW_UPDATE frame using
- *   `nghttp2_submit_window_update()` to that stream ID before
+ *   This function returns assigned stream ID if it succeeds.  But
+ *   that stream is not opened yet.  The application must not submit
+ *   frame to that stream ID before
  *   :member:`nghttp2_session_callbacks.before_frame_send_callback` is
- *   called for this frame.  Other types of frames can be submitted to
- *   the returned stream ID.
+ *   called for this frame.
  *
  */
 int32_t nghttp2_submit_request(nghttp2_session *session,
@@ -2369,11 +2367,9 @@ int nghttp2_submit_response(nghttp2_session *session,
  *
  *   This function returns assigned stream ID if it succeeds and
  *   |stream_id| is -1.  But that stream is not opened yet.  The
- *   application must not submit WINDOW_UPDATE frame using
- *   `nghttp2_submit_window_update()` to that stream ID before
+ *   application must not submit frame to that stream ID before
  *   :member:`nghttp2_session_callbacks.before_frame_send_callback` is
- *   called for this frame.  Other types of frames can be submitted to
- *   the returned stream ID.
+ *   called for this frame.
  *
  */
 int32_t nghttp2_submit_headers(nghttp2_session *session, uint8_t flags,
@@ -2542,6 +2538,14 @@ int nghttp2_submit_settings(nghttp2_session *session, uint8_t flags,
  * :enum:`NGHTTP2_ERR_INVALID_ARGUMENT`
  *     The |stream_id| is 0.
  *
+ * .. warning::
+ *
+ *   This function returns assigned promised stream ID if it succeeds.
+ *   But that stream is not opened yet.  The application must not
+ *   submit frame to that stream ID before
+ *   :member:`nghttp2_session_callbacks.before_frame_send_callback` is
+ *   called for this frame.
+ *
  */
 int32_t nghttp2_submit_push_promise(nghttp2_session *session, uint8_t flags,
                                     int32_t stream_id,