Fix outdated comment.

Multi-insert records observe XLOG_HEAP_INIT_PAGE flag too, as Andres Freund
pointed out.

src/include/access/htup.h

@@ -593,15 +593,15 @@ typedef HeapTupleData *HeapTuple;
 
 #define XLOG_HEAP_OPMASK		0x70
 /*
- * When we insert 1st item on new page in INSERT/UPDATE
- * we can (and we do) restore entire page in redo
+ * When we insert 1st item on new page in INSERT, UPDATE, HOT_UPDATE,
+ * or MULTI_INSERT, we can (and we do) restore entire page in redo
  */
 #define XLOG_HEAP_INIT_PAGE		0x80
 /*
  * We ran out of opcodes, so heapam.c now has a second RmgrId.	These opcodes
  * are associated with RM_HEAP2_ID, but are not logically different from
- * the ones above associated with RM_HEAP_ID.  We apply XLOG_HEAP_OPMASK,
- * although currently XLOG_HEAP_INIT_PAGE is not used for any of these.
+ * the ones above associated with RM_HEAP_ID.  XLOG_HEAP_OPMASK applies to
+ * these, too.
  */
 #define XLOG_HEAP2_FREEZE		0x00
 #define XLOG_HEAP2_CLEAN		0x10