[3772] Corrected documentation error in v6 configuration example

doc/guide/dhcp6-srv.xml

@@ -480,9 +480,11 @@ temporarily override a list of interface names and listen on all interfaces.
 	<screen>
 "Dhcp6": {
     "subnet6": [
-        "subnet": "2001:db8:1::/64",
-        <userinput>"id": 1024</userinput>,
-        ...
+        {
+            "subnet": "2001:db8:1::/64",
+            <userinput>"id": 1024</userinput>,
+            ...
+        }
     ]
 }
 </screen>