We check on start up that we don't have more antennas than max, so it is
useless to do it here.

We have usually two VFs per RU.

Let's assume we have currently one one RU (xran_port).

Then we need to have num_vfs == num_rus == num_dus

later we need to have num_vfs * xran_ports == num_rus == num_dus

(I think)