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

I tried to change rx and tx attenuation by the config file, but they are not changed. The bug is because att_rx and att_tx do not put in RC.rru when local_rf is "yes" in config file. We need to put att_rx and att_rx for both local_rf = "yes" and "no". Also RF config which send to RF device must be fill by this parameters.

The following compilation did not work anymore:

    ./build_oai --eNB -w USRP -r Rel10 -c

(Rel8 still does not work.)

Slave RU can now synchronize, the problem was in nb_antennas_rx which is init in UE but not in RU. I added it in ru_thread_control, but it should be done somewhere else. Added msg RRU_sync_ok from RRU to RAU to inform the RAU that the RRU is in sync

- add function free_td() -> complements init_td() [seems to not be used, added
  for completeness]
- add function free_td8() -> undoes init_td8() [free memory of 8-bit LLR Turbo
  decoder]
- add function free_td16() -> undoes init_td16() [free memory of 16-bit LLR
  Turbo decoder]
- change function free_tdavx216() -> undoes init_tdavx216() [free memory of
  16-bit LLR Turbo decoder, AVX2 version]
- add free_lte_top() -> frees memory allocated by init_lte_top()
- change free_ul_ref_sigs() to set freed pointers to NULL
- add method free_transport() -> frees memory of ULSCH/DLSCH transport channels
- use the above functions when stopping/restarting the lte-softmodem

this methods free the memory that is allocated by the functions
phy_init_RU() and phy_init_lte_eNB()

Through configuration, the lte-softmodem can be halted to await a
reconfiguration from the lte-softmodem. A mutex and condition variable are used
to implement this.

Furthermore, the dependance of lte-softmodem.c on FlexRAN has been reduced to
one include and the flexran_agent_start() call.

- add set_function_spec_param() which configures RU_t instance depending on its
  function(al split)
- export more functions like kill_RU_proc() so that they can be reused by
  restart functionality