vdpasim: fix MAC address configuration

vdpasim: fix MAC address configuration

vdpa_sim generates a ramdom MAC address but it is never used by upper
layers because the VIRTIO_NET_F_MAC bit is not set in the features list.

Because of that, virtio-net always regenerates a random MAC address each
time it is loaded whereas the address should only change on vdpa_sim
load/unload.

Fix that by adding VIRTIO_NET_F_MAC in the features list of vdpa_sim.

Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
Cc: jasowang@redhat.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Link: https://lore.kernel.org/r/20201029122050.776445-2-lvivier@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>