Support inheriting properties in channel programs

This adds support in channel programs to inherit properties analogous
to `zfs inherit` by adding `zfs.sync.inherit` and `zfs.check.inherit`
functions to the ZFS LUA API.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Jason King <jason.king@joyent.com>
Closes #9738

man/man8/zfs-program.8

@@ -9,8 +9,9 @@
 .\"
 .\"
 .\" Copyright (c) 2016, 2019 by Delphix. All Rights Reserved.
+.\" Copyright 2020 Joyent, Inc.
 .\"
-.Dd February 26, 2019
+.Dd January 15, 2020
 .Dt ZFS-PROGRAM 8
 .Os
 .Sh NAME
@@ -364,6 +365,27 @@ Valid only for destroying snapshots.
 If set to true, and the snapshot has holds or clones, allows the snapshot to be
 marked for deferred deletion rather than failing.
 .Ed
+.It Em zfs.sync.inherit(dataset, property)
+Clears the specified property in the given dataset, causing it to be inherited
+from an ancestor, or restored to the default if no ancestor property is set.
+The
+.Ql zfs inherit -S
+option has not been implemented.
+Returns 0 on success, or a nonzero error code if the property could not be
+cleared.
+.Pp
+dataset (string)
+.Bd -ragged -compact -offset "xxxx"
+Filesystem or snapshot containing the property to clear.
+.Ed
+.Pp
+property (string)
+.Bd -ragged -compact -offset "xxxx"
+The property to clear.
+Allowed properties are the same as those for the
+.Nm zfs Cm inherit
+command.
+.Ed
 .It Em zfs.sync.promote(dataset)
 Promote the given clone to a filesystem.
 Returns 0 on successful promotion, or a nonzero error code otherwise.