OpenZFS 7252 - compressed zfs send / receive

OpenZFS 7252 - compressed zfs send / receive
OpenZFS 7628 - create long versions of ZFS send / receive options

Authored by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed by: David Quigley <dpquigl@davequigley.com>
Reviewed by: Thomas Caputi <tcaputi@datto.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed by: David Quigley <dpquigl@davequigley.com>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Ported-by: bunder2015 <omfgbunder@gmail.com>
Ported-by: Don Brady <don.brady@intel.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting Notes:
- Most of 7252 was already picked up during ABD work.  This
  commit represents the gap from the final commit to openzfs.
- Fixed split_large_blocks check in do_dump()
- An alternate version of the write_compressible() function was
  implemented for Linux which does not depend on fio.  The behavior
  of fio differs significantly based on the exact version.
- mkholes was replaced with truncate for Linux.

OpenZFS-issue: https://www.illumos.org/issues/7252
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/5602294
Closes #6067

module/zfs/dmu.c

@@ -1889,6 +1889,10 @@ dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp,
 	boolean_t nopwrite = B_FALSE;
 	boolean_t dedup_verify = os->os_dedup_verify;
 	int copies = os->os_copies;
+	boolean_t lz4_ac = spa_feature_is_active(os->os_spa,
+	    SPA_FEATURE_LZ4_COMPRESS);
+
+	IMPLY(override_compress == ZIO_COMPRESS_LZ4, lz4_ac);
 
 	/*
 	 * We maintain different write policies for each of the following