Improved connection draining with small number of connections. Closing up to 32 connections might be too aggressive if worker_connections is set to a comparable number (and/or there are only a small number of reusable connections). If an occasional connection shorage happens in such a configuration, it leads to closing all reusable connections instead of gradually reducing keepalive timeout to a smaller value. To improve granularity in such configurations we now close no more than 1/8 of all reusable connections at once. Suggested by Joel Cunningham.

--- a/src/core/ngx_cycle.h
+++ b/src/core/ngx_cycle.h
@@ -53,6 +53,7 @@ struct ngx_cycle_s {
     ngx_uint_t                modules_used;    /* unsigned  modules_used:1; */
 
     ngx_queue_t               reusable_connections_queue;
+    ngx_uint_t                reusable_connections_n;
 
     ngx_array_t               listening;
     ngx_array_t               paths;