vdpa: Enable user to set mac and mtu of vdpa device

vdpa: Enable user to set mac and mtu of vdpa device

$ vdpa dev add name bar mgmtdev vdpasim_net mac 00:11:22:33:44:55 mtu 9000

$ vdpa dev config show
bar: mac 00:11:22:33:44:55 link up link_announce false mtu 9000

$ vdpa dev config show -jp
{
    "config": {
        "bar": {
            "mac": "00:11:22:33:44:55",
            "link ": "up",
            "link_announce ": false,
            "mtu": 9000,
        }
    }
}

Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20211026175519.87795-5-parav@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>