volinfo: print namei filenames of index files

On namei fileservers, also print the namei filenames of the volume special
files when the -header flag is given.

Reviewed-on: http://gerrit.openafs.org/4696
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 4999ed13d2355743e07587c8d7c4d23cbc073c5f)

Change-Id: I09c93c6b7512250f47359e70c5a744182ea91d9f
Reviewed-on: http://gerrit.openafs.org/11249
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>