This tracer extracts output subframes generated by the eNodeB,
so they can be analyzed with some external tools.

- UE_id 0 is for rnti 65535 (sib)
- UE_id 1 is for rnti 65534 (this is a hack)
- UE_id 2 is for rnti 2     (RA RNTI as of today's code/config)
- we start enb by displaying UE_id 3
- there was a bug: we need to lock when resetting UE ids (reset_ue_ids)

removal of LOG_I put for debugging.

remove getopt call in configuration module, it changes the argv order. Fix configuration module bugs (command line arguments sometimes not properly processed

not finished, UE may not work, many things bad/to fix properly

Improve configuration module error management at init time, Fix command line help option processing, remove shotopt field from parameter structure

Fix configuration module shared library improperly build and not loadable when libconfig version is below 1.5

lte-softmodem -O <config file> will trigger legacy config mode
ltesoftmodem  -O libconfig:<config file> will trigger configuration module usage.

- ENB_PHY_OUTPUT_SIGNAL to trace output signal
- ENB_MAC_SCHEDULING_REQUEST to trace scheduling requests

This program extracts a given subframe from a recorded trace.

Note: this commit is work in progress. Contains initial integration of NFAPI data structures which are tested for TX path. RX path to follow.

see https://gitlab.eurecom.fr/oai/openairinterface5g/issues/227

When the UE connects to the eNodeB and receives its IP address from the
network, it calls system() to set it in the linux kernel world. This call
is not done in a realtime thread, but in the NAS, which uses its own thread,
independent of the realtime processing.

In some situations this totally disrupts realtime processing.

It is difficult to know precisely why that happens, but it seems that calling
fork(), as system() does, in a multi-threaded program is not a good idea. (So
say several people on the internet.) It is not clear why the softmodem is
impacted, but it seems that fork() is really what triggers the disruption.
Several tests lead to that conclusion.

To fix the problem, we create a child background process very early in main()
(before anything else basically). Then instead of calling system(), the main
process sends the string to the background process. The background process
gets the string, passes it to system() and reports the success/failure back
to the main process.

This solution involves a lot of system calls, but calling system() in the
first place is not cheap either. As long as no realtime thread uses this
mechanism, things should be fine. Time will tell.

Prior to this commit, the following command failed to build dlsim:
    ./build_oai --phy_simulators -c

Choice has been made to define it in a .h file as a static inline
function.

We now have 4 versions of T_HEADER:
 - bad quality C++ version with time
 - good quality C version with time
 - bad quality C++ version without time
 - good quality C version without time

Adapt calling sites too.

When data comes from the user, it is good to check that
what we read is correct and warn the user if it's not.

we want those traces in the logs people send to us and
the group HEAVY is disabled in the wiki instructions.

looks better