SOLARIS: Support VSW_STATS

SOLARIS: Support VSW_STATS

Specify the VSW_STATS flag to the vfsdef_t structure we give to
Solaris. This turns on statistics that can be retrieved via fsstat(1M)
and allows the fsinfo::: DTrace provider to work with AFS files.

We don't need to actually maintain these statistics; Solaris does that
for us. This flag just signifies that our vfs_t structure is capable
of storing the information. Since we get our vfs_t from Solaris (via
domount(), it gives us a vfs_t when it calls our afs_mount function)
and do not allocate a vfs_t ourselves, we are safe and this is fine to
do.

Reviewed-on: http://gerrit.openafs.org/10679
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit b0f433986ce344bf153cce1f6372de20750e052b)

Change-Id: I2403703f9caeb190563360d8571ee0be46890f4d
Reviewed-on: https://gerrit.openafs.org/12371
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>