virtio_net: fix endian-ness for RSS

Using native endian-ness for device supplied fields is wrong
on BE platforms. Sparse warns about this.

Fixes: 91f41f01

 ("drivers/net/virtio_net: Added RSS hash report.")
Cc: "Andrew Melnychenko" <andrew@daynix.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>