get_default_secondaryCellGroup() would "sanitize" the servingCellConfig,
i.e., remove BWP that are invalid. However, it is difficult to
understand (we can do sanitization once at the beginning) and reason
(why the servingCellConfig is modified in
get_default_secondaryCellGroup(), because all we want is a new
CellGroupConfig, without modifying other data structures).

Instead, do sanitization once after reading the configuration in
gnb_config.c. Also, modify physical simulators nr_dlsim and nr_ulsim to
apply this sanitization before a call to
get_default_secondaryCellGroup(), as the latter would have done the
sanitization.