qemuDomainAttachNetDevice: Explicitly list allowed types for hotplug
    
    Instead of blindly claim support for hot-plugging of every
    interface type out there we should copy approach we have for
    device types: white listing supported types and explicitly error
    out on unsupported ones.
    For instance, trying to hotplug vhostuser interface results in
    nothing usable from guest currently. vhostuser typed interfaces
    require additional work on our side.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>