improve rfsim

Fix a regression: someone moved parameter reading in a external thread, so the check at the end of the main was too early, therefore declaring some extra paramters are on command line

Enhancement: use the rfsim as a server on UE side, so we can connect two xNB to one UE

simplification: remove rfsim flags that have been made for convergence with replay function in usrp driver, but won't be used as they changed their code

Fix a bug in ubuntu 20.04 (now the code is ready in whole OAI)