nwfilter: Remove 'qemu-announce-self' example

The example allows packets sent by qemu after migration with broken
protocol ID. The proper self announce is handled via
'qemu-announce-self-rarp'.

The qemu bug was addressed by f8778a7785d530515b0db39 (released as
v0.13.0). As we no longer support such old qemus, and allowing broken
packets makes no sense. Remove the rule and make it into an alias of
'qemu-announce-self-rarp' to preserve compatibility. Adjust the existing
examples to use only the proper rule.t

Closes: https://gitlab.com/libvirt/libvirt/-/issues/792
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

docs/firewall.rst

@@ -285,7 +285,6 @@ useful rules:
    fb57c546-76dc-a372-513f-e8179011b48a  no-mac-spoofing
    dba10ea7-446d-76de-346f-335bd99c1d05  no-other-l2-traffic
    f5c78134-9da4-0c60-a9f0-fb37bc21ac1f  no-other-rarp-traffic
-   7637e405-4ccf-42ac-5b41-14f8d03d8cf3  qemu-announce-self
    9aed52e7-f0f3-343e-fe5c-7dcb27b594e5  qemu-announce-self-rarp
 
 Most of these are just building blocks. The interesting one here is

docs/formatnwfilter.rst

@@ -438,7 +438,7 @@ several other filters.
      <filterref filter='allow-incoming-ipv4'/>
      <filterref filter='no-arp-spoofing'/>
      <filterref filter='no-other-l2-traffic'/>
-     <filterref filter='qemu-announce-self'/>
+     <filterref filter='qemu-announce-self-rarp'/>
    </filter>
 
 To reference another filter, the XML node ``filterref`` needs to be provided