Note: some modifications have been done to the UE too, but for syntactic
reasons. The UE may fail to work, not tested.

For the UE, we have the problem of handling properly SecurityModeCommand.
We don't verify its integrity. This is a bit complicated to handle properly
and may require some API changes in the PDCP layer. So, as of today, the
integrity of this message is not verified.

Also, NSA mode has been touched, but it should not be a problem. But not
tested, so not sure.

In the UE executable, delete the initialization of NR.nrrrc and check the NULL of NR.nrrrc

This reverts commit 64aa42d6

Enable IP TUN interface configuration upon reception of PDU Session Establishment Accept NAS message

-User plane traffic validation with OAI UE and OAI CN:

-Downlink ping initiated from the CN is received at the IP interface of the UE. However it seems that there is some packet corruption preventing the generaration of ping reply.

-Uplink ping initiated from the UE reaches the OAI CN machine. However no ping reply is seen yet either.

"infinity" is -1 in the code.

handling of SDAP header, move RAR to slot last DL slot in TDD period (need change in configuration file)

changes in gtpu interface for testing, small changes in L1 for PUSCH signal/noise measurements. SRB2 interfaces.

This commit implements integrity and security settings for nr pdcp. It will
only work for SRBs.

This commit has not been tested. It may fail to work completely. To be checked.

corrections in PUCCH handling for dedicated configuration on initialBWP. first transmission handling for DL harq processes at UE.

-RRCSetupComplete successfully transferred to RLC of the UE now through SRB1, but not at the MAC yet.
-Needed to enable some additional elements for RLC config. at the gNB side (asn1_msg.c) so that the addition of the SRB does not fail at the UE.
 To verify if these are really required.

The discard timer is used by the PDCP layer to discard packets that were not
transmitted to RLC after some time.

We don't really need it for the moment, maybe never for the default
bearer which is a best-effort bearer passing all kind of IP traffic.
Maybe for voice over IP kind of traffic it's important, or realtime
applications.

I ran an iperf UDP uplink test and saw no error on the PHY layer but still
lots of packets lost in the iperf logs, which was very surprising. By
analyzing the logs in wireshark I saw that, with the current scheduler,
an IP packet sent by the UE took 40ms to be sent piece by piece to the
gNB, and then the next uplink IP packet was never sent at all because
the discard timer was expired, leading to the high count of packets lost
in the iperf logs.

So let's put infinity for the moment for the discard timer. From my
understanding of the moment it's not a problem. If for some reason we
should set it to some non-infinity value, then we can change later.

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.

-For the moment SRBs are preconfigured (as was done for DRBs in noS1 mode)
but this should be removed

if the UE is running with noS1, u-plane for rfsim with Free5GC + CU/DU is OK