refine config, check the connections more precise

@@ -1489,23 +1489,21 @@ int SrsConfig::check_config()
         nb_consumed_fds += 3;
         
         int nb_connections = get_max_connections();
-        int nb_pipes = nb_connections * 2;
-        int nb_reserved = 10; // reserved
-        int nb_total = nb_connections + nb_pipes + nb_consumed_fds + nb_reserved;
+        int nb_total = nb_connections + nb_consumed_fds;
         
         int max_open_files = sysconf(_SC_OPEN_MAX);
-        int nb_canbe = (max_open_files - (nb_consumed_fds + nb_reserved)) / 3 - 1;
+        int nb_canbe = max_open_files - nb_consumed_fds - 1;
 
         // for each play connections, we open a pipe(2fds) to convert SrsConsumver to io,
         // refine performance, @see: https://github.com/winlinvip/simple-rtmp-server/issues/194
         if (nb_total >= max_open_files) {
             ret = ERROR_SYSTEM_CONFIG_INVALID;
             srs_error("invalid max_connections=%d, required=%d, system limit to %d, "
-                "total=%d(max_connections=%d, nb_pipes=%d, nb_consumed_fds=%d, nb_reserved=%d), ret=%d. "
+                "total=%d(max_connections=%d, nb_consumed_fds=%d), ret=%d. "
                 "you can change max_connections from %d to %d, or "
                 "you can login as root and set the limit: ulimit -HSn %d", 
                 nb_connections, nb_total, max_open_files, 
-                nb_total, nb_connections, nb_pipes, nb_consumed_fds, nb_reserved,
+                nb_total, nb_connections, nb_consumed_fds,
                 ret, nb_connections, nb_canbe, nb_total);
             return ret;
         }