openzfs_sysctl_init() now returns void instead of int.
The ZfsArcStats->enabled flag is set inside the init function
now, instead of having to be set from its return value.
Preparation for more flag setting in Compressed ARC commit.
ZfsArcMeter_readStats() added and all Meter->values[] setting
moved to it, eliminating duplicated code in
{darwin,freebsd,linux,solaris}/Platform.c.
If no pools are imported (ARC size == 0) or the
ZFS module is not in the kernel (/proc/spl/kstat/zfs/arcstats
does not exist), then the Meter reports "Unavailable".
New meter displays same ARC stats as FreeBSD top(1).
Can be extended to other platforms that support ZFS.
Pulling kstat.zfs.misc.arcstats.c_max as the meter
total, so the meter has a meaningful value to work
up to.
The Text meter displays, first, the maximum
ARC size (Meter.total), then second, the total
ARC used, using the difference between Meter.maxItems
and Meter.curItems to "hide" the used value from the
Bar and Graph drawing functions by using an index
in Meter.values[] that is beyond curItems - 1, but
less than maxItems - 1.
