Factor out opts parsing, clean up shutdown.

adsbus/opts.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <stdbool.h>
+
+bool opts_add_dump(char *);
+bool opts_add_connect_receive(char *);
+bool opts_add_connect_send(char *);
+bool opts_add_listen_receive(char *);
+bool opts_add_listen_send(char *);