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Running TCP DL traffic with one connected UE showed a lot of
fluctuations in throughput. After analysis it was found that
sometimes the RLC UM PDU was not correct. It contained one byte
more than it should. On the receiver side, the TCP packet
contained in the RLC packet seems to be rejected by the TCP
stack of the UE (it has one byte more than it should),
leading to a brutal reduction of the throughput, probably due
to some congestion detection in the TCP implementation.
Or something.

This hotfix seems to solve the problem. Using iperf in downlink
with a 5MHz eNB, we see no more fluctuations, the traffic is
very steady at 16.8Mb/s, as reported by the iperf server running
on the phone. (17.5 in the PHY plot of the T tracer.)

A rewrite of both the MAC and RLC UM packet generation is needed.
The code is way too complex for what it does and may contain
several similar problems that only trigger in specific rare
conditions.

Without this revert, the following does not compile:

    ./build_oai --oaisim

- remove spaces at the end of lines
- remove useless dead code
  use: git show -p <this commit> -w
  to see it clearly

Some more fixes for some bad conflict resolutions.

I ran:

    git diff 2018.w04 2018.w05

And saw some problems with config_sib2.

There was also something strange in openair2/LAYER2/openair2_proc.c
in the function dump_eNB_l2_stats. Maybe the fix is wrong for
this one. To be checked.

Doing an iperf UDP uplink test, we could reach only 6Mb/s
with very good radio conditions instead of around 8Mb/s.

It turns out the MCS was limited to 16.

With this commit, we are back to a bit more than 8Mb/s
as it used to be.

(This is with a 5MHz bandwidth.)

Doing airplane mode off to connect a cots UE followed by airplane mode on
to disconnect it gives very bad results (bad disconnection with lots of
UL failures followed by lots of logs in the eNB). It used to work properly
after the work done by Xu Bo.

It turns out that in 2018.w04 things were still working okay. But
in 2018.w05 no.

So I ran:

    git diff 2018.w04 2018.w05

And I checked all the modifications that I thought were relevant
(everything related to the UE, oaisim, if4 and fapi has not been checked).

This commits takes back the version of 2018.w04.

The modifications in openair2/RRC/LITE/rrc_eNB.c are necessary, I think.

The other modifications may not be necessary or even wrong. To be checked
at some point.

The problem that may happen is that when the UE does not transmit
on PUCCH (for whatever reason) we may get no signal at all, and
thus compute a very low CQI. Later on we may ask the UE to transmit
louder which may lead to saturation and more problems.

The solution is simple: don't care about CQI in case of DTX
(and NACK also, as done for PUSCH).

Only FDD case done.
For TDD it seems that:
- nfapi structures are not correct. See nfapi_harq_indication_tdd_rel13_t
  in nfapi/open-nFAPI/nfapi/public_inc/nfapi_interface.h, all the cases
  (bundling, multiplex, ...) use nfapi_harq_indication_tdd_harq_data_t
- the function extract_harq does not handle TDD

There is too much UL scheduling because the buffer status is
overestimated.

This commit tries to make things simpler.

The following compilation did not work anymore:

    ./build_oai --eNB -w USRP -r Rel10 -c

(Rel8 still does not work.)

all the FlexRAN scheduling code is now also handled by the general OAI
scheduling code

As reported by Emad Alizade:

    According to "Issue255 256 257 paging reesta release" that has been
    merged in develop version, we have a question: In rrc_eNB_free_UE()
    function only all ulsch related memory of user has been cleaned, but
    I think not only ulsch memory but also dlsch memory must be cleaned.
    I tested the latest develop version and with repetition UE attach-detach
    procedures we find that the dlsch memory has not been cleaned and after
    repeat this sequence (45 times) assertion with cause UE_id!=-1 (no free
    or exiting dlsch_context, dci_tools.c: fill_dci_and_dlsch() ) occurred
    and no UE will be attached to system.

The fixes in this commit are from Emad Alizade.