Implement initial shutdown + reconnect FSM

The shutdown_fsm doesn't do much right now, but it's included there in
order to allow easy clean up of resources upon Iuh reconnect in the
future, as well as reset the lower layers.

Change-Id: Id35d692218af366843186b0966b62f65bb9eb620

include/osmocom/hnodeb/hnodeb.h

@@ -26,6 +26,7 @@
 #include <osmocom/core/write_queue.h>
 #include <osmocom/core/logging.h>
 #include <osmocom/gsm/gsm23003.h>
+#include <osmocom/netif/stream.h>
 
 enum {
 	DMAIN,
@@ -62,6 +63,9 @@ struct hnb {
 
 	uint32_t ctx_id;
 
+	struct osmo_fsm_inst *shutdown_fi; /* FSM instance to manage shutdown procedure during process exit */
+	bool shutdown_fi_exit_proc; /* exit process when shutdown_fsm is finished? */
+
 	struct {
 		struct hnb_chan *chan;
 	} cs;