2 issues at this point:
1.rfsim for FR1 works sometimes. other times 100 consec PBCH errors.(this commit)
2.PDCCH and PDSCH are not transmitted in correct slots. problem might be with sf_ahead.

fix important bug in CU, merge thread pool improvement and rf simulator improvements made initialy in 5G branch

fix phy simulators build Pb: move snr_dB global to simulation code, add a channel mode section in configuration for snr_dB ,add a parameter flag in the config module to allow omitting prefix when modifying a parameter (for compatibility of -s option)

add channel model option to rfsimulator and prevent common libraries re-compilation when using both --UE --eNB options in build_oai script

add config options for rfsimulator, set a common lib for l1sim and rfsimulator, avoid simulation sources to be added twice in some execs (tau.c)

Fix a few cppcheck errors/warnings

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>