Gain settings for other sdr

[Brabudu]

The setting.xml file contains the gain settings but in the scripts the only useful one is the one for the rtl-sdr:
(from /scripts/receive_noaa.sh)
if [[ "$receiver" == "rtlsdr" ]]; then
gain_option="--gain"
ppm_correction="--ppm_correction"
else
gain_option="--general_gain"
FREQ_OFFSET=""
fi

The sdrplay instead, for example, uses lna_gain and if_gain.
It would be useful to include the possibility of better specifying these parameters without having to manually modify the script.