Added max_headers directive. The directive limits the number of request headers accepted from clients. While the total amount of headers is believed to be sufficiently limited by the existing buffer size limits (client_header_buffer_size and large_client_header_buffers), the additional limit on the number of headers might be beneficial to better protect backend servers. Requested by Maksim Yevmenkin.

--- a/src/http/ngx_http_core_module.h
+++ b/src/http/ngx_http_core_module.h
@@ -198,6 +198,8 @@ typedef struct {
 
     ngx_msec_t                  client_header_timeout;
 
+    ngx_uint_t                  max_headers;
+
     ngx_flag_t                  ignore_invalid_headers;
     ngx_flag_t                  merge_slashes;
     ngx_flag_t                  underscores_in_headers;