[core] default backend "connect-timeout" to 8 (#3086)

default backend "connect-timeout" to 8 seconds

Though this is is a behavior change where there previously was no
timeout, this is configurable by lighttpd.conf admin, and having a
default connection timeout of a fairly large value (8 seconds) puts
a (default) limit on resource usage waiting for socket connect().

x-ref:
  "sockets disabled, out-of-fds with proxy module"
  https://redmine.lighttpd.net/issues/3086

src/gw_backend.c

@@ -1389,6 +1389,7 @@ int gw_set_defaults_backend(server *srv, gw_plugin_data *p, const array *a, gw_p
             host->max_procs    = 4;
             host->max_load_per_proc = 1;
             host->idle_timeout = 60;
+            host->connect_timeout = 8;
             host->disable_time = 1;
             host->break_scriptfilename_for_php = 0;
             host->kill_signal = SIGTERM;