macvlan: change the max number of queues to 16

Macvtap should be at least compatible with tap, so change the max number to 16.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>