Implements a complex sample delay buffer integrated into the tuner

channel manager so that channel source requests can have a start
timestamp specified and the channel can be preloaded with samples from
the delay buffer.  If no timestamp is specified, current time is assumed.

This feature requires corresponding updates to any decoder that wishes
to implement the timestamped sample preloading functionality.

src/main/java/io/github/dsheirer/source/tuner/airspy/AirspyTunerController.java

@@ -107,6 +107,13 @@ public class AirspyTunerController extends USBTunerController
         mDevice = device;
     }
 
+    @Override
+    public int getBufferSampleCount()
+    {
+        //Each airspy complex sample is 4 bytes, so sample count is buffer size / 4
+        return USB_TRANSFER_BUFFER_SIZE / 4;
+    }
+
     public void init() throws SourceException
     {
         mDeviceHandle = new DeviceHandle();