[Enhancement] bias-T option for rtl_fm

[AgriVision]

In order to power a pre-amplifier with the bias-T this option needs to be added to the rtl_fm command.

$rtl_fm -h
...........
[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]
............

e.g. in sat.sh:
timeout $5 rtl_fm -p "${RTL_PPM}" -f "${FREQ}M" -s "${rxbw}" -T\

or via user.conf:
BIAST=-T
sat.sh:
timeout $5 rtl_fm -p "${RTL_PPM}" -f "${FREQ}M" -s "${rxbw}" "${BIAST}"\

[stdevPavelmc]

Good catch!

I will work on it as time permit...