SoapyLMS7 setBandwidth() improvements and FIR filter

[guruofquality]

Thoughts on doing a better job of implementing automatic and manual filter settings, any comments are appreciated: Currently the setBandwidth() function tries to set the baseband filter only. But the analog filter range will not always go as low as requested. Perhaps instead, the analogue BW should be set in accordance with the TSP rate. And then the FIR filters could be set to match the requested bandwidth within the TSP rate. And then when the requested BW is larger than the TSP rate, we can go back to the current behaviour or bypass the FIR filters.