So since there are now three radios (that I know) that has a hardware Bias T support (HackRF, RTLSDR, Airspy) I added a set_biast and get_biast methods to the default Source API. I also added Airspy and HackRF bindings to enable / disable Bias T. The RTLSDR isn't merged into mainstream, so I didn't added anything.

There is also the default implementations (doing nothing for set, and returning false for get), so no breaks on the current source or current applications.