MFC r230514:

MFC r230514:
Merge illumos revisions 13572, 13573, 13574:

Rev. 13572:
disk sync write perf regression when slog is used post oi_148 [1]

Rev. 13573:
crash during reguid causes stale config [2]
allow and unallow missing from zpool history since removal of pyzfs [5]

Rev. 13574:
leaking a vdev when removing an l2cache device [3]
memory leak when adding a file-based l2arc device [4]
leak in ZFS from metaslab_group_create and zfs_ereport_checksum [6]

References:
https://www.illumos.org/issues/1909 [1]
https://www.illumos.org/issues/1949 [2]
https://www.illumos.org/issues/1951 [3]
https://www.illumos.org/issues/1952 [4]
https://www.illumos.org/issues/1953 [5]
https://www.illumos.org/issues/1954 [6]

Obtained from:	illumos (issues #1909, #1949, #1951, #1952, #1953, #1954)

git-svn-id: svn://svn.freebsd.org/base/stable/8@231142 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f