Update httpd.conf.j2

The current `Listen` directive does not work on systems that have ipv6 disabled. The Apache Listen directive supports `Listen <port>` syntax at which point it seems to be able to listen correctly on both dual stack and ipv4 only systems. See https://httpd.apache.org/docs/2.4/bind.html for more details.

ironic-config/httpd.conf.j2

@@ -1,6 +1,6 @@
 ServerRoot "/etc/httpd"
 {%- if env.LISTEN_ALL_INTERFACES | lower == "true" %}
-Listen [::]:{{ env.HTTP_PORT }}
+Listen {{ env.HTTP_PORT }}
 {% else %}
 Listen {{ env.IRONIC_URL_HOST }}:{{ env.HTTP_PORT }}
 {% endif %}