OpenZFS 6536 - zfs send: want a way to disable setting of DRR_FLAG_FREERECORDS

Authored by: Andrew Stormont <astormont@racktopsystems.com>
Reviewed by: Anil Vijarnia <avijarnia@racktopsystems.com>
Reviewed by: Kim Shrier <kshrier@racktopsystems.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/6536
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/880094b

include/sys/zfs_ioctl.h

@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
+ * Copyright 2016 RackTop Systems.
  */
 
 #ifndef	_SYS_ZFS_IOCTL_H
@@ -136,6 +137,10 @@ typedef enum dmu_send_resume_token_version {
 
 #define	DMU_BACKUP_MAGIC 0x2F5bacbacULL
 
+/*
+ * Send stream flags.  Bits 24-31 are reserved for vendor-specific
+ * implementations and should not be used.
+ */
 #define	DRR_FLAG_CLONE		(1<<0)
 #define	DRR_FLAG_CI_DATA	(1<<1)
 /*