nwfilter: Remove 'qemu-announce-self' example

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>