Linux: change test for new putname API

Linux: change test for new putname API

Replace the existing test with a more robust one that checks for
the existence of the new filename structure.  Since older kernels
are expected to fail this test, we'll get the correct result even
if there is unrelated failure, for instance a missing/different
header file.

Reviewed-on: http://gerrit.openafs.org/8466
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 2bafb2f99d85804459acb8994d4057be809f8729)

Change-Id: I88536425612e39b2f7d4d09c51ce896bc8cf6d4f
Reviewed-on: http://gerrit.openafs.org/8559
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Hans-Werner Paulsen <hans@MPA-Garching.MPG.DE>
Tested-by: Hans-Werner Paulsen <hans@MPA-Garching.MPG.DE>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>