In multiRU we will need to be able to check multiple radio units for RX saturation separately.

-> As a preparatory step adjust the SR to explicitly specify the list of RX antennas to be verified.

This patch is necessary because in nexedi/slapos.toolbox!126
we adjust check_rx_saturated plugin to require list of RX channels to check to be
explicitly specified.

/cc @tomo, @xavier_thompson, @Daetalus
/reviewed-by @jhuge, @lu.xu
/reviewed-on nexedi/slapos!1459