* This change is backwards compatible and checks for API support for step size.
* Created soapy_common.cc/h to house common gain range functions
* Moved factory mutex declaration to common source files as well
Switch to the newer API call which can provide a list of ranges.
There are feature detection ifdefs provided by the library
so that code will always correctly compile.
The soapysdr range type does not provide a step size,
however apps like the osmocom siggen use this size for a slider,
and a value of zero will cause a divide by zero error.
Although many ranges are not actually linear,
the idea to provide some default step to avoid crashes.
A future addition to the API may include providing a step.
When the special 0.0 bandwidth setting is used, set the filter bandwidth to rate * 0.75.
Passing automatic 0.0 bandwidth for some devices was problematic.
Josh Blum