Add code to accept MAC configuration through vdpa tool. The MAC is
written into the config struct and later can be retrieved through
get_config().

Examples:
1. Configure MAC while adding a device:
$ vdpa dev add mgmtdev pci/0000:06:00.2 name vdpa0 mac 00:11:22:33:44:55

2. Show configured params:
$ vdpa dev config show
vdpa0: mac 00:11:22:33:44:55 link down link_announce false max_vq_pairs 8 mtu 1500
Signed-off-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20211026175519.87795-8-parav@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>