Move adsbus into its own dir.

adsbus/airspy_adsb.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <stdbool.h>
+
+struct buf;
+struct packet;
+
+void airspy_adsb_init();
+bool airspy_adsb_parse(struct buf *, struct packet *, void *);
+void airspy_adsb_serialize(struct packet *, struct buf *);