Update all the SDR implementation to use it.
This was getting pretty ugly with code getting copy&pasted in all the SDR
implementations. Unify it all and give it a simpler API. Linked list works out
much simpler than the circular buffer. Also, simplify copying the overlap region
around by just using a separate buffer (it's only a few hundred bytes long, so
the double copy is not a big deal).
In cases where we do get an odd-length buffer (_very_ rare!)
it seems to be more about dropped USB data and not librtlsdr giving
us a partial callback; subsequent callbacks will still be aligned
with the I byte first despite the odd count.
Oliver Jowett
Rosen Penev
Oliver Jowett
Mictronics