Now that the nwfilter driver keeps a list of bindings that it has
created, there is no need for the complex virt driver callbacks. It is
possible to simply iterate of the list of recorded filter bindings.

This means that rebuilding filters no longer has to acquire any locks on
the virDomainObj objects, as they're never touched.
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>