promise/plugin/check_rx_saturated: Don't hardcode "all rx antennas" as a set of what to check

Currently check_rx_saturated checks saturation on all rx antennas. This
works well for ORS, which has only one SDR board, but won't work for
multiRU case where we will need to check RX for saturation for each
Radio Unit separately.

-> As a preparatory step adjust check_rx_saturated to take list of which
RX antennas to check for saturation.

For now this change is accompanied by the following change in
ors-amarisoft SR to keep it working as before:

    --- a/software/ors-amarisoft/instance-enb.jinja2.cfg
    +++ b/software/ors-amarisoft/instance-enb.jinja2.cfg
    @@ -699,6 +699,7 @@ config-stats-period = {{ slapparameter_dict.get("enb_stats_fetch_period", 60) }}
     <= macro.promise
     promise = check_rx_saturated
     config-testing = {{ slapparameter_dict.get("testing", False) }}
    +config-rf-rx-chan-list = {{ list(range(0, int(slapparameter_dict.get('n_antenna_ul', default_n_antenna_ul)))) }}
     config-amarisoft-stats-log = ${amarisoft-stats-template:log-output}
     config-stats-period = {{ slapparameter_dict.get("enb_stats_fetch_period", 60) }}
     config-max-rx-sample-db = {{ slapparameter_dict.get("max_rx_sample_db", 0) }}

(posted in slapos!1459)

/cc @lu.xu, @xavier_thompson, @Daetalus
/reviewed-by @jhuge
/partly-reviewed-by @tomo
/reviewed-on !126