When rebuilding oaisim, I had a failure because the target
link already exists. The -f flag forces the link to be done.

- some cleanup
- thread names to include UE Mod_id
- arg of UE_thread_rxn_txnp4 to be struct rx_tx_thread_data again
- sync in UE_thread_rxn_txnp4 to use instance_cnt_rxtx again
- UE_thread to call itti_send_msg_to_task with UE->Mod_id + NB_eNB_INST
  instead of INSTANCE_DEFAULT again

This may break the softmodem UE, to be tested.
The most problematic thing may be the synchronization.
I don't think it will impact the processing at all,
but I won't bet my shirt on it.

git show -p 58052152
to see what it's about

git show 157707b0
to see what it's about

Many variables were changed that should not have been changed.

This reverts commit d31634c3.

Laurent Thomas had a problem on one machine with the build_oai
way of checking for nettle.

The problem with the alternative solution of including nettle/bignum.h
is that it is very unclear.

The problem with nettle is that the file nettle/config.h does not
exist for version 2. It was introduced in version 3.

We want to support both versions, but there is an API incompatibility.
So we need an #if #else mechanism.

The file nettle/bignum.h is present in both versions 2 and 3 and it
includes nettle/version.h in the version 3.

So by including this file, we can check for the existence of
NETTLE_VERSION_MAJOR (that comes from nettle/config.h) in the
code.

But as you can see, the reasoning is way too complex.

So it's better to keep the check in cmake_targets/CMakeLists.txt.

As long as we support version 2 this will be the way to go.

It is possible to force a given version in specific non-generic
customized environments.

Conflicts:
	targets/RT/USER/lte-enb.c
	targets/RT/USER/lte-softmodem.c
	targets/RT/USER/lte-ue.c

Memory was allocated which was "lost" because the
address of the block was put in a pointer that is
overwritten just after.

Discussing with Elena, the current commit is the correct
way to do things.

Those functions modify a global char array (a string).

Let's pass a buffer to those functions, so that it's
thread safe. The caller has been modified, with hopefully
a buffer big enough (still bigger than what was there before,
so should not break more than it did).

command run:
    dos2unix openair1/SIMULATION/TOOLS/taus.c

 Conflicts:
	openair1/SCHED/phy_procedures_lte_ue.c
	targets/RT/USER/lte-softmodem.c
	targets/SIMU/USER/oaisim.c
	targets/SIMU/USER/oaisim_functions.c

This commit follows 7d9945e8.

lte-softmodem UE in S1 and lte-softmodem UE in noS1 modes behave
differently here.

This commit fixes the issue for thoses cases.

Other cases (eNB S1, eNB noS1, oaisim S1/noS1) have to be checked.

- fix OPc key
- clear EHPLMN_LIST, UE does not start the RA procedure when set
  to be fixed

This commit is a continuation of 614d6bbe
(ue_ip: use correct instance).

Now in openair2/NETWORK_DRIVER/UE_IP/common.c the 'inst' is not
forced to 1 anymore, we take the value 'pdcph_p->inst'.

It turns out that 'pdcph_p->inst' is 0 instead of 1 when we
run lte-softmodem as an UE.

So let's modify PDCP to set 'inst' to 1 where it was set to 0 for
the UE softmodem case, and skip the places where it is reset to 0,
still for the UE softmodem case.

This may break things, I am not sure.

Guess what happens when we return from the function...

For whatever reason, lte-softmodem.c was totally messed up...

We took the version from the branch develop and added
abstraction_flag, which is needed in openair2/LAYER2/MAC/main.c
(this is not clean, previous commit added a comment for this).
This has to be cleaned at some point.

- the option --UE was abused! Let's introduce --UE-conf-nvram and
  --UE-gen-nvram
- the option name --UE-OUTPUT was not clear and is now replaced by
  --UE-gen-nvram
- the new options are described when running ./build_oai -h
- print_help has been modified (' replaced by ") to print
  $conf_nvram_path and $gen_nvram_path

Conflicts:
	openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c
	openair1/PHY/LTE_TRANSPORT/power_control.c
	openair2/LAYER2/MAC/eNB_scheduler_dlsch.c
	targets/SIMU/USER/oaisim_functions.c

The problem was the following.

Run oaisim with two UEs:

    sudo ../cmake_targets/oaisim_build_oai/build/oaisim -O enb.conf -u2 -s15 -AAWGN -y1 -b1 -Q0

Then wait for both UEs to be connected. The interfaces "oip1" and "oip2" are
activated, with IP addresses 192.172.0.2 for the first UE and 192.172.0.3 for
the second.

Then on the EPC machine, do:

    ping 192.172.0.3

No reply.
On the oaisim machine, we see that the packets are sent to "oip1" instead
of "oip2".

The fix may break softmodem UE. The inst was forced to "1" for some reason.
To be checked.

The memset was also too big. It should only clear
one subframe.

Only tested without abstraction.
Abstraction does not work for the moment anyway, but just to
keep that in mind.

The idea is as follows.

oaisim waits for all tasks to be done for a TTI.
To do so it waits for last_rx_timestamp == current_rx_timestamp,
for all UEs and eNBs.

When it's done, it increases current_rx_timestamp by samples_per_tti,
to inform UEs and eNBs that a new TTI is ready.

In the functions [UE|eNB]_trx_read, we wait for a new TTI to be ready,
that is we wait for current_rx_timestamp != last_rx_timestamp.

The UE has also to wait for processing threads to be done.
In the eNB it's not necessary because the processing is all
done in one thread, that is: read subframe, process this subframe,
emit subframe+4, and then back to read subframe.

The code is not clean. We should not use usleep but semaphores.

Also, do_[DL|UL]_sig should not read from rxdata and write to txdata,
but use internal buffers.

The functions [UE|eNB]_trx_read should call do_[DL|UL]_sig and then
copy from the internal buffers of the channel simulator into rxdata.

The functions [UE|eNB]_trx_write should write data passed into the
internal buffers of the channel simulator.