OpenZFS 5120 - zfs should allow large block/gzip/raidz boot pool (loader project)

Authored by: Toomas Soome <tsoome@me.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Andrew Stormont <andyjstormont@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Don Brady <don.brady@intel.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting Notes:
- grub-2.02-beta2-422-gcad5cc0 includes support for large blocks.
- Commit 8aab121 allowed GZIP[1-9].
- Grub allows pools with multiple top-level vdevs.

OpenZFS-issue: https://www.illumos.org/issues/5120
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/c8811bd
Closes #6007

module/zfs/spa.c

@@ -26,6 +26,8 @@
  * Copyright (c) 2013, 2014, Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright 2013 Saso Kiselkov. All rights reserved.
+ * Copyright (c) 2014 Integros [integros.com]
+ * Copyright 2016 Toomas Soome <tsoome@me.com>
  * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
@@ -534,12 +536,6 @@ spa_prop_validate(spa_t *spa, nvlist_t *props)
 				    &propval)) == 0 &&
 				    !BOOTFS_COMPRESS_VALID(propval)) {
 					error = SET_ERROR(ENOTSUP);
-				} else if ((error =
-				    dsl_prop_get_int_ds(dmu_objset_ds(os),
-				    zfs_prop_to_name(ZFS_PROP_RECORDSIZE),
-				    &propval)) == 0 &&
-				    propval > SPA_OLD_MAXBLOCKSIZE) {
-					error = SET_ERROR(ENOTSUP);
 				} else if ((error =
 				    dsl_prop_get_int_ds(dmu_objset_ds(os),
 				    zfs_prop_to_name(ZFS_PROP_DNODESIZE),