Do not do it this way, run lighttpd strictly as a daemon. The daemon xinetd is mean to start services that are not actually running all the time. When xinetd sees traffic it "spins up" a particular service to meet the need, but otherwise the processes are not running.
By the way, you cannot share a TCP port between 2 daemons/services. Only one service can bind to a particular TCP port, essentially owning it for the duration of the time that it's running.