MFC r272884:

accept(2) may and can return EAGAIN, document it.
MFC r272504: MFV r272494:

Make space_map_truncate() always do space_map_reallocate().  Without
this, setting space_map_max_blksz would cause panic for existing pool,
as dmu_objset_set_blocksize would fail if the object have multiple blocks.

Illumos issues:
   5164 space_map_max_blksz causes panic, does not work
   5165 zdb fails assertion when run on pool with recently-enabled
	spacemap_histogram feature
MFC r272507: MFV r272496:

Add tunable for number of metaslabs per vdev
(vfs.zfs.vdev.metaslabs_per_vdev).  The default remains
at 200.

Illumos issue:
    5161 add tunable for number of metaslabs per vdev
MFC r272510: MFV r272498:

Add a new sysctl, vfs.zfs.vol.unmap_enabled, which allows the system
administrator to toggle whether ZFS should ignore UNMAP requests.

Illumos issue:
    5149 zvols need a way to ignore DKIOCFREE
MFC r272511: MFV r272499:

Illumos issue:
    5174 add sdt probe for blocked read in dbuf_read()
MFC r272584: MFV r272501:

Illumos issue:
    5177 remove dead code from dsl_scan.c
MFC r272598: MFV r272585:

Split the godfather zio into CPU number's to reduce lock
contention.

Illumos issue:
    5176 lock contention on godfather zio
MFC r272599: MFV r272588:

Handle old format deadlist.

Illumos issue:
    5178 zdb -vvvvv on old-format pool fails in dump_deadlist()
MFC r272601: MFV r272591:

Use loaned ARC buffer for zfs receive to avoid copy.

Illumos issue:
    5162 zfs recv should use loaned arc buffer to avoid copy
MFC r273204:
  Add more descriptive metadata to the ISO images.

Sponsored by:	The FreeBSD Foundation
Fix label for the UEFI bootonly cd.

Sponsored by:	The FreeBSD Foundation
MFC r272721:
  Fix a long standing bug in MAC statistics register access.  One
  additional register was erroneously added in the MAC register set
  such that 7 TX statistics counters were wrong.
MFC r272729,272732:
  Add new quirk PCI_QUIRK_MSI_INTX_BUG to pci(4).
  QAC AR816x/E2200 controller has a silicon bug that MSI interrupt
  does not assert if PCIM_CMD_INTxDIS bit of command register is set.
Merge remote-tracking branch 'freebsd/stable/10' into freebsd10