virtio_net: fix adding vids on big-endian

Programming vids (adding or removing them) still passes
guest-endian values in the DMA buffer. That's wrong
if guest is big-endian and when virtio 1 is enabled.

Note: this is on top of a previous patch:
	virtio_net: split out ctrl buffer

Fixes: 9465a7a6 ("virtio_net: enable v1.0 support")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>