NR: fix time keeping in RLC for gNB

RLC has timers. We need to keep track of time. We chose to not use realtime but 'processing time'. That is we send a tick to RLC for every subframe when it is processed by the softmodem. Before this commit we used to increase time in the function mac_rlc_status_ind which is called for every subframe in the eNB, but not in the gNB (at least not in the current gNB). So we need another way to keep track of time.

The function gNB_dlsch_ulsch_scheduler is called for every slot. It seems to be the perfect candidate to send a tick to RLC for every subframe. We take care of subcarrier spacing to send every subframe (one subframe is always 1ms), not every slot (slot duration depends on subcarrier spacing).

It may not be the best solution. To be revised if needed.

Note: the UE has not been fixed. Some modification is needed for the UE too, most probably.