Description of problem:

The xvfb-run "-l" or "--listen-tcp" option does not work

Version-Release number of selected component (if applicable):

xorg-x11-server-Xvfb-1.20.11-9.el8.x86_64

How reproducible:

Always

Steps to Reproduce:
1. Install xorg-x11-server-Xvfb and xterm

2. Log in via GDM

3. Open a gnome-terminal window and run this test command:

   $ xvfb-run -d -l -s "-ac" bash -c "export DISPLAY=localhost\$DISPLAY; xterm -e 'echo hello;sleep 1';"

Actual results:

   xterm: Xt error: Can't open display: localhost:2

Expected results:

xterm should run using a Xvfb server that listens at localhost, port 6002.

Additional info:

As a workaround, it's possible to pass "-isten tcp" to Xvfb:

   $ xvfb-run -d -l -s "-ac -listen tcp" bash -c "export DISPLAY=localhost\$DISPLAY; xterm -e 'echo hello;sleep 1';"

The cause of the problem is that when we pass "-l" or "--listen-tcp" to
xvfb-run it sets the LISTENTCP variable to empty:

LISTENTCP="-nolisten tcp"
...
while :; do
    case "$1" in
        -a|--auto-servernum) SERVERNUM=$(find_free_servernum) ;;
        -d|--auto-display) AUTO_DISPLAY=1 ;;
        -e|--error-file) ERRORFILE="$2"; shift ;;
        -f|--auth-file) AUTHFILE="$2"; shift ;;
        -h|--help) SHOWHELP="yes" ;;
        -n|--server-num) SERVERNUM="$2"; shift ;;
        -l|--listen-tcp) LISTENTCP="" ;;
        -p|--xauth-protocol) XAUTHPROTO="$2"; shift ;;
        -s|--server-args) XVFBARGS="$2"; shift ;;
        -w|--wait) STARTWAIT="$2"; shift ;;
        --) shift; break ;;
        *) error "internal error; getopt permitted \"$1\" unexpectedly"
           exit 6
           ;;
    esac
    shift
done

Starting on RHEL 8, however the X server (including Xvfb) does not listen on a
TCP port by default, as it did up to RHEL 7. So it would be necessary to set
LISTENTCP to "-listen tcp".

The problem happens on RHEL 9 too, for the same reason.