zfs.8 has wrong description of "zfs program -t"

zfs.8 has wrong description of "zfs program -t"

The "-t" argument to "zfs program" specifies a limit on the number of
LUA instructions that can be executed.  The zfs.8 manpage has the wrong
description.  It should be updated to match what's in zfs-program.8

Also fix the formatting of the zfs help message.

Reviewed by: Allan Jude <allanjude@freebsd.org>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #8410