Select rtlsdr versoin by device number

[gariac]

It would be useful if the rtlsdr version could select by device number.

[wcampbell0x2a]

You should be able to use --driver-extra like #102

[gariac]

Like they say on reddit, today I learned there are commands for soapysdr:

https://github.com/charlie-foxtrot/RTLSDR-Airband/wiki/Configuring-SoapySDR-devices

This will give me some things to hack. I have one of those Chinese MSI devices I could never get running. Thanks.