MFV r247174:

Expose arc_meta_limit, et al via kstats.

Note that as a result, vfs.zfs.arc_meta_used is removed.
The existing vfs.zfs.arc_meta_limit sysctl/tunable is retained
with a SYSCTL_PROC wrapper.

Illumos ZFS issues:
    3561 arc_meta_limit should be exposed via kstats

Relnotes:	yes
MFC after:	2 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275748 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f