docs: add an IPv6 address to network XML examples

It was just pointed out that, although I added documentation for the
IPv6 additions to the network XML, I neglected to use those additions
in the examples. This patch adds an IPv6 address to each of the
examples except for the "default" network, since that is a faithful
reproduction of the default network config that's automatically
installed, which doesn't include any IPv6 address (for good reason -
because there is no such thing as IPv6 NAT, there is no one IPv6
address that would work for all installations).

docs/formatnetwork.html.in

@@ -121,6 +121,7 @@
             <host mac="00:16:3e:3e:a9:1a" name="bar.example.com" ip="192.168.122.11" />
           </dhcp>
         </ip>
+        <ip family="ipv6" address="2001:8794:ca2:2::1" prefix="64" />
       &lt;/network&gt;</pre>
 
     <dl>
@@ -226,6 +227,7 @@
             &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
           &lt;/dhcp&gt;
         &lt;/ip&gt;
+        &lt;ip family="ipv6" address="2001:8794:ca2:2::1" prefix="64" /&gt;
       &lt;/network&gt;</pre>
 
     <h3><a name="examplesRoute">Routed network config</a></h3>
@@ -249,6 +251,7 @@
             &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
           &lt;/dhcp&gt;
         &lt;/ip&gt;
+        &lt;ip family="ipv6" address="2001:8794:ca2:2::1" prefix="64" /&gt;
       &lt;/network&gt;</pre>
 
     <h3><a name="examplesPrivate">Isolated network config</a></h3>
@@ -270,6 +273,7 @@
             &lt;range start="192.168.152.2" end="192.168.152.254" /&gt;
           &lt;/dhcp&gt;
         &lt;/ip&gt;
+        &lt;ip family="ipv6" address="2001:8794:ca2:3::1" prefix="64" /&gt;
       &lt;/network&gt;</pre>
 
   </body>