Develop integration w13

Summary of changes:
- RLC AM reworking (a lot has changed)
- several bug fixes
  * support processing multiple MAC RAR control elements in a single MSG2
  * fix ACK/NACK resetting
  * do not correct USRP frequency from carrier offset estimation when --ue-carrier-scan == off
  * fix TDD uplink due to incorrect PUCCH format for SR in TDD
  * several other simple fixes
- better support for LMS SDR

See merge request !168

- define _GNU_SOURCE before including pthread.h
- do not use static for the array 'threadname' used
  to store the name, it makes it a global variable
  accessed by several threads in parallel
- increase size of 'threadname' (maybe not necessary)
- properly indent #define / #under (# should be at column 1)

When you ran it with the scope as:

    ./dlsim -X

you saw no activity in the "PDSCH I/Q of MF Output" window,
so matter what SNR you put (even for very high SNR, say: ./dlsim -X -s40)

this commit seems to fix it.

I am not sure it is the end of story. The 2 threads PDCCH/PDSCH structures
may still not be used correctly everywhere.

#221 fixed RRC crash when parsing the RRCConnectionReconfiguration message with empty neighCellConfig in measObjectEUTRA

We have a strange problem with the timestamp of the very
first packets received from the LimeSDR that leads to
a complete failure of the eNB.

A simple workaround is to discard the first RX packet
just after a "start" of the device.

We also change the value of "tx_sample_advance" to a more
reasonable value. The problem of timestamp was "solved"
differently in the past and at the time we needed to put
a much higher value.

This may have to be refined at some point.