Make opaque_data parameter in nghttp2_submit_goaway const

lib/includes/nghttp2/nghttp2.h

@@ -2230,7 +2230,7 @@ int nghttp2_submit_ping(nghttp2_session *session, uint8_t flags,
  */
 int nghttp2_submit_goaway(nghttp2_session *session, uint8_t flags,
                           nghttp2_error_code error_code,
-                          uint8_t *opaque_data, size_t opaque_data_len);
+                          const uint8_t *opaque_data, size_t opaque_data_len);
 
 /**
  * @function

lib/nghttp2_session.c

@@ -4650,7 +4650,8 @@ int nghttp2_session_add_ping(nghttp2_session *session, uint8_t flags,
 int nghttp2_session_add_goaway(nghttp2_session *session,
                                int32_t last_stream_id,
                                nghttp2_error_code error_code,
-                               uint8_t *opaque_data, size_t opaque_data_len)
+                               const uint8_t *opaque_data,
+                               size_t opaque_data_len)
 {
   int rv;
   nghttp2_frame *frame;

lib/nghttp2_session.h

@@ -274,7 +274,8 @@ int nghttp2_session_add_ping(nghttp2_session *session, uint8_t flags,
 int nghttp2_session_add_goaway(nghttp2_session *session,
                                int32_t last_stream_id,
                                nghttp2_error_code error_code,
-                               uint8_t *opaque_data, size_t opaque_data_len);
+                               const uint8_t *opaque_data,
+                               size_t opaque_data_len);
 
 /*
  * Adds WINDOW_UPDATE frame with stream ID |stream_id| and

lib/nghttp2_submit.c

@@ -167,7 +167,7 @@ int nghttp2_submit_rst_stream(nghttp2_session *session, uint8_t flags,
 
 int nghttp2_submit_goaway(nghttp2_session *session, uint8_t flags,
                           nghttp2_error_code error_code,
-                          uint8_t *opaque_data, size_t opaque_data_len)
+                          const uint8_t *opaque_data, size_t opaque_data_len)
 {
   return nghttp2_session_add_goaway(session, session->last_stream_id,
                                     error_code, opaque_data, opaque_data_len);