Rework on audio interface

Sound instance is now called audio instance and uses funcation pointers.
This gives a clean interface to be exchanged with other technologies,
linke SDR.

src/bnetz/dsp.c

@@ -388,7 +388,7 @@ again:
 		memset(samples, 0, length * sizeof(*samples));
 		break;
 	case DSP_MODE_AUDIO:
-		jitter_load(&bnetz->sender.audio, samples, length);
+		jitter_load(&bnetz->sender.dejitter, samples, length);
 		break;
 	case DSP_MODE_0:
 		fsk_tone(bnetz, samples, length, 0);