Implement data transfer (38.331 5.2):
    - transmit operation (in nr_pdcp_entity_recv_sdu)
    - receive operation (in nr_pdcp_entity_recv_pdu)
    - t-Reordering expiration

To keep track of time the function nr_pdcp_wakeup_timer_thread has been
added and is called by the gNB's MAC scheduler via nr_pdcp_tick.

(The UE has not been modified.)

A thread has been introduced to set time of all the existing PDCP
entities in the system. This probably does not scale well with many
PDCP entities (many UEs connected to the gNB). To be changed at some
point when needed. Hopefully, with a few UEs this mechanism won't be
too problematic (ie. won't cause realtime problems).

The problem with time in PDCP is that SDUs are kept if some are
missing, to do reordering. A timer is started and when it expires
we have to transmit the SDUs even if some are still missing. We
want to do that as soon as possible. So we have to check timers
often (every millisecond).

In RLC the time is set when there is some activity (SDU or PDU
received). In PDCP we cannot wait for this kind of activity. We
would keep packets longer than necessary, which may disturb
upper layers (think: TCP). That is why we introduced the thread,
as a simple mechanism to keep packets no longer than necessary.

The locking done by this thread may create realtime issues.

The whole logic of time keeping can be changed later if it turns
out that it is not efficient.

The functions dealing with DRB AM have been removed. All the types
of PDCP entities (DRB AM, DRB UM, SRB) use the same mechanism for
transmit and receive operations. So the code has been made common
for all those types.

We don't deal with:
    - entity re-establishment, entity release or entity suspend
    - SDU discard (the timer is present but not used)
    - status reporting
    - data recovery
    - data volume calculation
    - header compression / decompression

There is no plan to implement those features in a near future.

Integrity protection is not done yet, and will be implemented soon.

# Conflicts:
#	openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_ulsch.c

MR1029 : Benetel driver update  
This MR fixes an issue with the driver for the 4G Benetel RRUs.
Power levels on the 5G side were adapted to avoid saturation of the signals. 
5G performance is now the same as with USRP. 
Support for 2 antennas for both 4G and 5G was added

MR1062 : fixing the RE offset for each Rx antenna in pusch channel estimation

MR1046 : Add support for NR UL SC-FDMA up to 100 MHz

MR1053Nr : pdcp nea2 security

MR1049 : improve rfsim
-Fix a regression 
Earlier parameter reading was moved to an external thread,  
Eventually the check at the end of the main was too early, 
Declaration of  some extra parameters are now on command line
-Enhancement: 
use the rfsim as a server on UE side, so we can connect two xNB to one UE
-Simplification: 
remove rfsim flags that have been made for convergence with replay function in usrp driver, but this is useless as they changed their code
-Fix a bug in ubuntu 20.04 (now the code is ready in whole OAI)


MR1056 : Bugfix: NR BSR calculation
Fixes a bug in the scheduler for BSR calculation. 
Before, we might wrongly track the BSR of a UE and not schedule it anymore although it has data. 
Should be fixed now and improve UL throughput. 

MR963 : Nr mac multi rach global edge
-Handling of Multiple Users triggering RACH request in different RACH Occasions in same slot
-Providing Random Access Response according to RACH request

fixing the RE offset for each Rx antenna in pusch channel estimation

# Conflicts:
#	cmake_targets/CMakeLists.txt
#	openair1/SIMULATION/NR_PHY/dlsim.c
#	openair1/SIMULATION/NR_PHY/ulsim.c

MR978 : 
We have incorporated 5G NR nFAPI into the develop branch
P5 and P7 interfaces for NR have been implemented. 
With this MR, downlink transmission through nFAPI will be possible. 
We have also made sure that 4G nFAPI can be used from within the develop branch.

reducing UL target power for Benetel 5G RRU and adding missing parameter for PUSCH multi thread processing

1) Only count new transmission as scheduled bytes (which is then
compared against the BSR)

2) When subtracting scheduled bytes after successful reception, subtract
TBsize from correct HARQ process

go figure...

Dirty!

Dirty.

Dirty...

- a new section in the configuration file to select security algorithms,
  with new code to deal with it
- cleanup CG-ConfigInfo: specs seem to indicate that we must not
  add mcg_RB_Config; the gNB has to deal with that
- as a consequence, modify fill_default_rbconfig() that is called in
  every cases and needs security and bearer parameters

The new section in the configuration file looks like:

    security = {
      # preferred ciphering algorithms
      # the first one of the list that an UE supports in chosen
      # valid values: nea0, nea1, nea2, nea3
      ciphering_algorithms = ( "nea0", "nea2" );

      # preferred integrity algorithms
      # the first one of the list that an UE supports in chosen
      # valid values: nia0, nia1, nia2, nia3
      integrity_algorithms = ( "nia0" );
    };

The code is forced to use nea2, no matter what the UE supports.

After 2^18 PDCP packets, it will fail to work (we don't use HFN yet).

These limitations will be fixed in later commits.

The existing security function was not reused, because it does too
much memory allocation and initializes the security context at each
ciphering. So here comes nr_pdcp_security_nea2_cipher(). And also
the ciphering is done inplace. To be changed if necessary.