HTTP: change default response code when rate-limiting requests.

Previously, "503 Service Unavailable" response code was used, but
the new "429 Too Many Requests" response code is more appropriate.

Change-Id: I00dc197f3d5dd1c2085b21f15eeed854b9facb4f
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://nginx-review.googlesource.com/2523
Reviewed-by: Gurgen Hrachyan <gugo@google.com>

src/http/modules/ngx_http_limit_req_module.c

diff --git a/src/http/modules/ngx_http_limit_req_module.c b/src/http/modules/ngx_http_limit_req_module.c
index 2f695f2..ec3aadf 100644
--- a/src/http/modules/ngx_http_limit_req_module.c
+++ b/src/http/modules/ngx_http_limit_req_module.c
@@ -712,7 +712,7 @@
                                 NGX_LOG_INFO : conf->limit_log_level + 1;
 
     ngx_conf_merge_uint_value(conf->status_code, prev->status_code,
-                              NGX_HTTP_SERVICE_UNAVAILABLE);
+                              NGX_HTTP_TOO_MANY_REQUESTS);
 
     return NGX_CONF_OK;
 }