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.

Change-Id: Ie50abce37580eab803e9b07e636a1538f4a91a81
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>