domain_conf: Add configs for virtio net RSS and Hash report.

domain_conf: Add configs for virtio net RSS and Hash report.

Added "rss" and "rss_hash_report" configuration that should be
used with qemu virtio RSS. Both options are triswitches. Used as
"driver" options and affects only NIC with model type "virtio".
In other patches - options should turn on virtio-net RSS and hash
properties.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>