otherwise, if we only have a (negative) SR, the UE did not send
anything, and the PUCCH CQI is invalid

1: there can be 2bits AckNack + SR in PUCCH F0
2: when allocating csi_pucch, zero out struct
3: Make unfree resources a warning
4: When asserting, explain the issue

- Configure PUCCH Format 0 to be in separate RBs (each UE has dedicated
  resources)
- Configure RA preamble to be different per UE
- Configure CSI offset such that no two UEs have their report in the
  same frame

Nb_ue is not unique among UEs: consider 2 UEs present. The last UE has
CSI idx "2". Now the first UE disconnects, and a new UE connects. It
will also get CSI idx "2", and I assume this is not what we want.

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Integration Branch : 2021 week 14

See merge request oai/openairinterface5g!1121

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Mohammed Ismail <mohammed.ismail@openairinterface.org>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

The bug was:
connect a phone, disconnect, repeat five times. The fifth time the phone
does not reconnect because there is no free RA process.

When an UE is removed, we have to free associated RA processes.