Doesn't compile RTL support without modification.

[grmrgecko]

I had to comment out #ifdef LIBUSB_FOUND in-order to make gr-baz support rtl devices. now that I have done this, I found it doesn't support R820T. I see all you have done was C++ified osmocom's rtl-sdr. So I'll just do the same for the R820T driver.

[balint256]

Thanks for raising this issue - I also found this bug and have committed the fix! Let me know if works for you if you can.
Will have a look at the R820T code, very kind of you to do that :)