qemu: don't strip audio elements with user config present

qemu: don't strip audio elements with user config present

To support backwards live migration we must strip the default added
audio element, however, we are too aggressive in doing so. We are only
comparing a couple of attributes for equality, so risk stripping config
that was user customized. To improve this we need to a deep comparison
of the audio config.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>