fixed channel model initialization in rfsimulator for added parameter (to be added to bridge structure still)

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

update configuration file gnb.band78.tm1.106PRB.usrpx300.conf based on gnb.band78.tm1.106PRB.usrpn300.conf

adding executional option for usrp trx thread and adding null device function for device other than usrp

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

Instead of looping over UEs and all DL config Req/HI DCI0, loop first
over all DL config Req/HI DCI0, and for each, match UE.  Lowers CPU
traffic for high traffic situations.

UE_list_t is now used as a separate list. It can be e.g. used in the
scheduler to mark groups of users. The original UE_list_t is renamed to
UE_info_t to reflect that it is a container for information about UEs.

ignoring command line paramters clock_source and time_source in lte-softmodem and harmonizing it with nr-softmodem
time_source and clock_source handled separately in usrp_lib.cpp