httpd_sess_close: Check for session validity before closing

httpd_sess_close: Check for session validity before closing

If httpd_sess_trigger_close() gets called twice for the same socket,
the first httpd_sess_close() cb closes the correct socket, but the second
invocation closes the wrong socket which was just accepted and added to
the socket db. Checking for the lru counter will help identify this as the
counter is set only for requests actually served.