Add support for zpool user properties
Usage:
zpool set org.freebsd:comment="this is my pool" poolname
Tests are based on zfs_set's user property tests.
Also stop truncating property values at MAXNAMELEN, use ZFS_MAXPROPLEN.
Co-authored-by: Mateusz Piotrowski <0mp@FreeBSD.org>
Obtained from: OpenZFS 8eae2d214cfa Add support for zpool user properties
Sponsored by: Beckhoff Automation GmbH & Co. KG.
Sponsored by: Klara Inc.