news: Document kernel requirements for virtual networks

After 7431b3eb libvirt requires "filter", "nat" and
"mangle" tables to exist for both IPv4 and IPv6. This fact was
missed in the news.xml and since we don't have any better place
to advertise that let's update old news.

This was refined in 686803a1 and since that is not released
yet create a new entry documenting the refinement.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/news.xml

@@ -124,6 +124,18 @@
           Report class information for PCI node device capability.
         </summary>
       </change>
+      <change>
+        <summary>
+          Split setup of IPv4 and IPv6 top level chain
+        </summary>
+        <description>
+          The requirement resulting from private chains improvement done
+          in <code>v5.1.0</code> was refined so that only tables from
+          corresponding IP version are required. This means that if a
+          network doesn't have <code>IPv6</code> enabled then those
+          tables are not required.
+        </description>
+      </change>
     </section>
     <section title="Bug fixes">
     </section>
@@ -202,7 +214,9 @@
           Historically firewall rules for virtual networks were added
           straight into the base chains. This works but has a number of
           bugs and design limitations. To address them, libvirt now puts
-          firewall rules into its own chains.
+          firewall rules into its own chains. Note that with this change the
+          <code>filter</code>, <code>nat</code> and <code>mangle</code> tables
+          are required for both <code>IPv4</code> and <code>IPv6</code>.
         </description>
       </change>
       <change>