Added deactivating bias-T in rtl_(adsb|fm|power|tcp) on exit.

[kukabu]

Hello

The bias-T voltage was staying on after rtl tools ended. This is dangerous and can lead to damage device.

[erikarn]

+1 - this would be great to add as well!

[steve-m]

Agreed, could you move this to the deinitialization routine of librtlsdr instead of every commandline utility?

[erikarn]

I can take a crack at that if you'd like! I just need to make sure we hook SIGTERM properly.