MFV r249332 (illumos-gate 14005:55fc53126003)

Illumos ZFS issues:
  3654 zdb should print number of ganged blocks

MFC after:	2 weeks

(cherry picked from commit eb4f9057bf87c3d2dadbc85111c8ee74097cc6b3)
MFV r267565:

4757 ZFS embedded-data block pointers ("zero block compression")
4913 zfs release should not be subject to space checks

MFC after:	2 weeks

(cherry picked from commit f95fd16f8d88667bcf37bb162d3f8fcc9f888cc7)

Ticket: #5415
 - Fix handling of "new" style of ioctl in compatiblity mode [1];
 - Reorganize code and reduce diff from upstream;
 - Improve forward compatibility shims for previous kernel;

Reported by:	sbruno [1]
X-MFC-With:	r268075

(cherry picked from commit be1d315a0495d0ceec39374f3f49a5674595bf93)

Ticket: #5415
MFV r267566:

4390 i/o errors when deleting filesystem/zvol can lead to space map corruption

MFC after:	2 weeks

(cherry picked from commit 0d7d731791d57691c640cdbdae4769591b0f68eb)

Ticket: #5415
MFV r267567:

4881 zfs send performance degradation when embedded block pointers are
     encountered

illumos/illumos-gate@06315b795c0d54f0228e0b8af497a28752dd92da

MFC after:	2 weeks

(cherry picked from commit ebdbb8771cd798ea14224eb4499d960a2aa18565)

Ticket: #5415
MFV r267568:

4891 want zdb option to dump all metadata

illumos/illumos-gate@df15e419cb7359ba56ddddab9045e438d89e7cbc

MFC after:	2 weeks

(cherry picked from commit 5f023415af5aa5803be6fbd6e2760782f4a6ad53)

Ticket: #5415
MFV r267569:

4897 Space accounting mismatch in L2ARC/zpool

illumos/illumos-dist@3038a2b421b40dc5ac11cd88423696618584f85a

MFC after:	2 weeks

(cherry picked from commit 86aaa1302935ae7a1c050a36860cc802ae335dd6)

Ticket: #5415
MFV r267570:

4756 metaslab_group_preload() could deadlock

illumos/illumos-gate@30beaff42d8240ebf5386e8b7a14e3d137a1631f

MFC after:	2 weeks

(cherry picked from commit 0b2372b19519751cb4401277788ddabf61585521)

Ticket: #5415
MFV r268119:

4914 zfs on-disk bookmark structure should be named *_phys_t

illumos/illumos-gate@7802d7bf98dec568dadf72286893b1fe5abd8602

MFC after:	2 weeks

(cherry picked from commit 6012f0ab3a6d68d680ff3f02df97deb938177c2c)

Ticket: #5415
MFV r268121:

4924 LZ4 Compression for metadata

illumos/illumos-gate@b8289d24d866c1af02d7007348f7f057693c15d3

MFC after:	2 weeks

(cherry picked from commit 3218d43e56858300ce0f3750a0863debe8192c28)

Ticket: #5415
MFV r268122:

4929 want prevsnap property

illumos/illumos-gate@b461c7460e5e77cf65f00151162e654220c6e2fb

MFC after:	2 weeks

(cherry picked from commit ff95e6ff7f15e80345f114ebf0db450c0e226fd8)

Ticket: #5415