Our driver sets a mac if the HW is 00:..:00 so we need to be sure to
advertise VIRTIO_NET_F_MAC even if the HW doesn't.  We also need to be
sure that virtio_net sees the VIRTIO_NET_F_MAC and doesn't rewrite the
mac address that a user may have set with the vdpa utility.

After reading the hw_feature bits, add the VIRTIO_NET_F_MAC to the driver's
supported_features and use that for reporting what is available.  If the
HW is not advertising it, be sure to strip the VIRTIO_NET_F_MAC before
finishing the feature negotiation.  If the user specifies a device_features
bitpattern in the vdpa utility without the VIRTIO_NET_F_MAC set, then
don't set the mac.

Fixes: 151cc834 ("pds_vdpa: add support for vdpa and vdpamgmt interfaces")
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Message-Id: <20230711042437.69381-3-shannon.nelson@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>