Add option to disable Doppler tuning

[csete]

Original request: https://community.libre.space/t/keep-the-downlink-constant/5686

[dl7oap]

Thank you very much for opening this feature request. :-)

I would like to mention that doppler tuning should not be completely deactivated. The downlink should be constant, so the doppler correction must be done entirely on the uplink.

i think you know what i mean.

[csete]

Thanks for the clarification, Andy. From an implementation point of view, we will make it so that the Doppler can be disabled for both uplink and downlink individually.