slotmap: Log file/line when changing state

Change-Id: Idc7b350b464ddc50076f92dae592a0d5ad4d486a
diff --git a/src/debug.h b/src/debug.h
index 02551eb..e3994b4 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -1,4 +1,5 @@
 #pragma once
+#include <osmocom/core/logging.h>
 
 enum {
 	DMAIN,