Add MLINKs for all functions described in the libxo manpages.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275480 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Add to CTL support for threshold notifications for file-backed LUNs.

Previously it was supported only for ZVOL-backed LUNs, but now should work
for file-backed LUNs too.  Used value in this case is a space occupied by
the backing file, while available value is an available space on file
system.  Pool thresholds are still not implemented in this case.

MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275481 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f