Avoid using multicast addresses for Ethernet MAC examples

* docs/formatdomain.html.in: use '00:11:22:33:44:55' instead of
  '11:22:33:44:55:66'

docs/formatdomain.html.in

@@ -649,7 +649,7 @@
     <interface type='network'>
       <source network='default'/>
       <target dev='vnet7'/>
-      <mac address="11:22:33:44:55:66"/>
+      <mac address="00:11:22:33:44:55"/>
     </interface>
   </devices>
   ...</pre>
@@ -685,7 +685,7 @@
     &lt;interface type='bridge'&gt;
       &lt;source bridge='br0'/&gt;
       &lt;target dev='vnet7'/&gt;
-      &lt;mac address="11:22:33:44:55:66"/&gt;
+      &lt;mac address="00:11:22:33:44:55"/&gt;
     &lt;/interface&gt;
   &lt;/devices&gt;
   ...</pre>
@@ -707,7 +707,7 @@
     &lt;interface type='user'/&gt;
     ...
     &lt;interface type='user'&gt;
-      &lt;mac address="11:22:33:44:55:66"/&gt;
+      &lt;mac address="00:11:22:33:44:55"/&gt;
     &lt;/interface&gt;
   &lt;/devices&gt;
   ...</pre>