rename `OBJ_ITER_FINAL` to `OBJ_ITER_END` for clarity

We use the `final` argument in object iteration to denote
`OC_F_PRIVATE | OC_F_HFM | OC_F_HFP`.

As we now have `VDP_END` to mark the final bit of data, so should the
iterator flag be named `_END`. This also parallels `VDP_FLUSH` vs.
`OBJ_ITER_FLUSH`.

Supported by martin

Ref #3298

bin/varnishd/cache/cache.h

@@ -710,7 +710,7 @@ const void *ObjGetAttr(struct worker *, struct objcore *, enum obj_attr,
 typedef int objiterate_f(void *priv, unsigned flush,
     const void *ptr, ssize_t len);
 #define OBJ_ITER_FLUSH	0x01
-#define OBJ_ITER_FINAL	0x02
+#define OBJ_ITER_END	0x02
 
 int ObjIterate(struct worker *, struct objcore *,
     void *priv, objiterate_f *func, int final);

bin/varnishd/storage/storage_simple.c

@@ -261,7 +261,7 @@ sml_iterator(struct worker *wrk, struct objcore *oc,
 		VTAILQ_FOREACH_SAFE(st, &obj->list, list, checkpoint) {
 			u = 0;
 			if (VTAILQ_NEXT(st, list) == NULL)
-				u |= OBJ_ITER_FINAL;
+				u |= OBJ_ITER_END;
 			if (final)
 				u |= OBJ_ITER_FLUSH;
 			if (ret == 0 && st->len > 0)