vdpa_sim: store parsed MAC address in a buffer

As preparation for the next patches, we store the MAC address,
parsed during the vdpasim_create(), in a buffer that will be used
to fill 'config' together with other configurations.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20201215144256.155342-11-sgarzare@redhat.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>