This is taken from commit 7bc14347
and is necessary for the UE to function properly.

Whenever the value T_BUFFER_MAX changes, the tracers had to
be recompiled. The only reason why it was needed is because we
used some fixed size buffers to read events. This commit removes
this restriction.

Also, with the basic simulator, this value T_BUFFER_MAX now comes
with an #ifdef which would have required some special hackish-level
tricks in the tracers, which is not good.

Let's just allocate memory when needed.

This commit introduces a 'basic simulator'.

This basic simulator is made of:
- the standard eNB code using a special driver that mimics the USRP driver
- the standard UE code using a special driver that mimics the USRP driver
- no channel simulation
- some special code to deal with faster-than-realtime behaviour of this
  basic simulator

It connects one UE to one eNB. It requires an EPC, populated with the
correct configuration for the UE.

This is the initial release and may contain bugs (most probably race
conditions due to the faster-than-realtime behaviour).

To use it, see the documentation at:
    targets/ARCH/tcp_bridge/README.tcp_bridge_oai.

It has been tested with 25, 50 and 100 RBs, FDD mode.
(No check at all has been done to know if it could work in TDD mode.)

Summary of changes:
- some work on better parallel processing of eNB
  try the eNB with options: --fepw --codingw
- small changes for multi-UE simulation and simulation accuracy
  (UE power levels)
- initial work for the UE to use TUN device instead of ue_ip.ko
  only done for oaisim, default bearer, compile with:
    ./build_oai --ue-nas-use-tun <rest of options>

158 does not work well with the eNB softmodem.

- fix compilation of dlsim/ulsim/oaisim by defining some needed
  global variables
- fix compilation of oaisim: compile coding and params_libconfig
- fix running of if4p5 with low CPU count (oaisim was not working
  on the machine 'haswell' because of this)

Merge remote-tracking branch 'origin/RU-RAU-split-parallel-EMUFH-phy-test-merge' into develop_integration_2018_w15

modifications for simulator : power normalizations for UE TX, small changes to SNR targets for power control, default UE power (23 dBm now)

This work is based on work by NTT.

To use the code, do:
./build_oai --oaisim --ue-nas-use-tun -t ETHERNET -c

This commit only handles oaisim in S1 mode.

We won't handle noS1 mode.

Summary of changes:
- free configmodule memory when shutting down
  It is possible to restart the lte-softmodem via the FlexRAN controller.
  For this to work, the end_configmodule() method needs to be called when
  shutting the lte-softmodem down so that the configuration can be read
  again during a restart.
- Feature agent
  Implements an agent ID, consisting of the OAI module ID, the OAI eNB ID
  and the cell ID. The agent reads this information in its configuration
  read function and forwards it to the controller.
  This MR also contains some code forwarding SI info to the controller.
- various bugs fixed
  - remove start_background_system from eNB softmodem
  - fix memory leak when doing traffic
  - disable ITTI dump (does someone uses this?)
  - disable U-plane inactivity timer: it's very simple to put this back,
    but as of now it comes with its own problems that we don't have time
    to check/fix

Only ulsim and dlsim compile. The others (dlsim_tm4 pucchsim prachsim
pdcchsim pbchsim mbmssim) have been disabled.

Command line to compile: ./build_oai --phy_simulators

This is only needed by the UE code, to setup IP settings.
The eNB does not need this. (To be reverted if this is
wrong.)

When doing TCP downlink traffic with iperf for several
hours, the memory consumption of lte-softmodem does not
stop to grow.

After analysis, this commit seems to be the only fix needed.
To be checked somehow.

If anyone needs it, it's a simple matter of reverting this
basic commit.

It is annoying and does not seem to work properly.
To be checked/reworked if needed.

Keep in mind that we also want oaisim to be functional.

if the FlexRAN agent is disabled, do not read all the data and skip reading
of more information

The agent_id is a uint64 consisting of: module ID (i.e. mod_id, the several
instances of OAI at once, 16 bit), the enb_id from the configuration file (32
bit) and the cell_id from the configuration file (16 bit).

The module ID is part of the agent ID but it is easier to have it directly in
the struct.

It is possible to restart the lte-softmodem via the FlexRAN controller. For
this to work, the end_configmodule() method needs to be called when shutting
the lte-softmodem down so that the configuration can be read again during a
restart.