improvements for 4-layer MIMO at gNB

common/utils/nr/nr_common.c

common/utils/nr/nr_common.h

doc/FEATURE_SET.md

openair1/PHY/INIT/nr_init.c

openair1/PHY/NR_TRANSPORT/pucch_rx.c

openair1/SIMULATION/NR_PHY/pbchsim.c

openair2/LAYER2/NR_MAC_COMMON/nr_mac.h

openair2/LAYER2/NR_MAC_COMMON/nr_mac_common.c

openair2/LAYER2/NR_MAC_UE/config_ue.c

openair2/LAYER2/NR_MAC_UE/config_ue_sl.c

openair2/LAYER2/NR_MAC_gNB/config.c

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_primitives.c

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

openair2/RRC/NR/nr_rrc_config.c

openair2/RRC/NR/nr_rrc_proto.h

openair2/RRC/NR/rrc_gNB.c