Split init and config USRP device. It seems to have solved the stop/restart RAU without stopping the RRU

Merge branch 'ru_rau_enhancement' of https://gitlab.eurecom.fr/oai/openairinterface5g into ru_rau_enhancement

Merge branch 'ru_rau_enhancement' of https://gitlab.eurecom.fr/oai/openairinterface5g into ru_rau_enhancement

Merge branch 'ru_rau_enhancement' of https://gitlab.eurecom.fr/oai/openairinterface5g into ru_rau_enhancement

Merge branch 'ru_rau_enhancement' of https://gitlab.eurecom.fr/oai/openairinterface5g into ru_rau_enhancement

Conflicts:
	targets/SIMU/USER/oaisim.c

Dealing with connection lost case. Now the RRU keeps working but we can't restart it again, a problem with the USRP load

Summary of changes:
- a lot of work on flexran
- several compilation bugfixes
- some bugfixes for some bad conflict resolutions
- various bugs fixed

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.)

The following compilation failed before this commit:

    ./build_oai --eNB -w USRP -c --T-tracer

The following compilation did not work anymore:

    ./build_oai --eNB -c -w USRP --noS1

Neither did:

    ./build_oai --UE --noS1

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 functions are meant to restart the lte-softmodem (lower layers) and are not
supported in oaisim. They are provided to make oaisim compile.

- move IMSI extraction code to function, remove FLEXRAN comp. directive
- refactor the code, esp. don't do deep if-nesting
- remove m-tmsi part (does not give correct value)
- copy complete IMSI info to UE context, decode in RAN API