slotmap: Add _slotmap_del() for callers that already have a lock

Change-Id: Id05872c3676d0afe4c7abe74677fee62b4f03e53
diff --git a/src/slotmap.h b/src/slotmap.h
index a26de6d..3eb976f 100644
--- a/src/slotmap.h
+++ b/src/slotmap.h
@@ -81,6 +81,7 @@
 
 /* thread-safe removal of a bank<->client map */
 void slotmap_del(struct slotmaps *maps, struct slot_mapping *map);
+void _slotmap_del(struct slotmaps *maps, struct slot_mapping *map);
 
 /* initialize the entire map collection */
 struct slotmaps *slotmap_init(void *ctx);