Skip RAW kstat sysctls by default

Skip RAW kstat sysctls by default

hese kstats are often expensive to compute so we want to avoid them
unless specifically requested.

The following kstats are affected by this change:

kstat.zfs.${pool}.multihost
kstat.zfs.${pool}.misc.state
kstat.zfs.${pool}.txgs
kstat.zfs.misc.fletcher_4_bench
kstat.zfs.misc.vdev_raidz_bench
kstat.zfs.misc.dbufs
kstat.zfs.misc.dbgmsg

PR:		249258
Reported by:	mjg
Reviewed by:	mjg, allanjude
Obtained from:	https://github.com/openzfs/zfs/pull/11099
Sponsored by:	iXsystems, Inc.