[op25-dev] OP25 trunking updates for RTL SDR

The RTL SDR sticks as mentioned seem to have delays when changing frequency that cause lost calls in trunking mode. I've added a new feature (updated in git branch max-trunking-update2 and in the wiki) which uses a software Local Oscillator instead of hardware retuning which essentially makes tuning instantaneous. There is a restriction that all of the channels to be tuned including the trunk CC must fall inside the tuning passband (whose width is equal to the sampling rate). See the SignalScope wiki page for more information. Outside of this, LSM trunking works very well now with RTL SDR Max