This commit repairs the reestablishment after the introduction of the CU
UE ID in the CU, different from the DU UE ID. Now, the CU uses an
identifier different from the RNTI, used in the MAC, to refer to UEs.

To repair the reestablishment, a number of changes needed to be
introduced:

- Handle old_gNB_DU_UE_id in MAC

The MAC handles the old_gNB_DU_UE_id field in the DL RRC Message. The
commit adds encoding/decoding of the field. The MAC will drop the old
UE, but retain the CellGroup of the corresponding UE(!). Because a UE
releases the spCellGroup on reestablishment, the MAC does the same; it
needs to reapply the old configuration after a reconfiguration. For the
latter, introduce new variables to keep a "future" CellGroupConfig to be
applied (reconfigCellGroup) and a flag (expect_reconfiguration) that
applies the CellGroupConfig if a DL RRC Message transfer on DCCH, which
is assumed to be the reconfiguration.

- Add RNTI change in RLC

The RLC needs to reuse the old UE context. Hence, we simply change the
RNTI in the old context, and delete the new one.

- No PDCP UE ID change

The previous implementation of the PDCP used the RNTI; hence, the ID
needed to be switch (as above for the RLC). Since the PDCP now also uses
the CU UE ID, no identifier change is needed, and we remove all
corresponding code.

- No MAC modifications/update from CU

As foreseen by the spec, the CU does not modify or change the
cellGroupConfig in the RRC during reestablishment. This change will be
generalized in the future to all of the RRC.  Also, the
nr_rrc_mac_remove_ue() function has been removed: the MAC handles any UE
changes autonomeously, without being triggered from the RRC explicitly.

- Remove reestablish_rnti_map

The RRC does not use RNTIs for UE identification. Hence, a
reestablish_rnti_map to link two UEs to each other is not necessary
anymore.

After a reestablishment, the PDCP sequence number counters have to be
reset. Implement an API to allow the RRC to reset the sequence numbers
for a particular UE in the case of reestablishment

Plugin can trigger reestablishment (on DU)
and show counters of reestablishment (on CU)

The RRC gives its own RRC UE ID. It won't intervene if DUs assign the same RNTI to different UEs: it simply does not care what the DUs do with the RNTI.

- Use the same CU-UP in E1 as in CU-CP: we don't have a separate entity
  to allocate IDs, and we just use the same as the CU-CP
- Correct gNB CU-UP/CP UE IDs in E1AP message types to 32bit
- Set CU UP UE ID explicitly for clarity
- Remove RNTI from E1 messages, E1 does not know what an RNTI is

The UE had a list of known UEs. With the introduction of a separate
module for F1 UE ID handling that is also used in monolithic (to
separate CU UE ID from DU UE ID), this functionality is not needed, and
deleted in this commit.

Previously, the F1AP handler called various functions directly, instead
of sending an ITTI message to the RRC thread. This has two drawbacks:
- it can lead to data races if the RRC task uses functionality that is
  being accessed by the F1 task through this function
- no homogeneity: all other handlers send an ITTI message, so this one
  should too

- The CU/DU UE ID is used in DL RRC Message Transfer
- Note: The CU UE ID currently is still the RNTI
- on every DL RRC Message, the DU verifies that the UE exists
- Refactor RRC: common function to forward protected SRB PDUs

The RRC uses gNB_ue_ngap_id as its primary ID; the following commits
will introduce the usage of the (F1) gNB CU UE ID. This commits renames
the gNB_ue_ngap_id to rrc_ue_id to better reflect its usage as the RRC's
primary UE ID.

It will be used as the NGAP and F1 (CU) UE IDs.

To avoid 0 in the ID

for reusing the old UE Context after reestablishment: we have to free a
UE context, but that also free's the RA process that we still need.
Remove here

Is this necessary?

integration_2023_w31

See merge request oai/openairinterface5g!2282

* !1932 Introduce basic unit testing framework, cleanup
* !2259 NR_UE: improve NFAPI_NR_DMRS_TYPE1_linear_interp()
* !2271 Draft: Make asn1c debug traces functional
* !2274 remove NR UE RRC sub state
* !2278 CI: AW2S - update of AmariUE commands
* !2004 Fix gNB LLR plot view
* !2265 chore(ci): adding back LTE-UE Radio tests
* !2268 fix for PDCCH unscrambling at UE
* !2269 fixes for PUCCH F1 at UE
* !2258 pdcp_config_req_asn1 bug fix
* !2263 UE ServingCellConfigCommon cleanup
* !2275 Fix RRC UE timers based on frames and not slots
* !2280 handle scheduling of DLSCH with DCI10 in common search
* !2277 CI: no Jenkins mail, iperf refactor, add Quectel E1 test
* !2260 Preparation of release v2.0.0

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

Merge remote-tracking branch 'origin/NR_MAC_gNB_handle_DLSCH_with_DCI10_common_SS' into integration_2023_w31

- throughput test in DL
- UL throughput: 30s is enough
- increase bidir test time for more reliable measurement
- increase retx thresholds: 1% for first round is too low