Linux: stop trying to use getname/putname

The current code has afs_putname defined as

    kmem_cache_free (names_cachep, (void *) name);

This is wrong and will cause a double -free when syscall auditing is
enabled. Fix it to call putname properly.

Instead of that, just create a new afs_getname function that doesn't
bother with struct filename at all, and use that unconditionally.

Signed-off-by:Jeff Layton <jlayton@redhat.com>

Change-Id: I1cd58a7e528abfeb7473cf47ae4cff5b8c8f419c
Reviewed-on: http://gerrit.openafs.org/10547
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeff Layton <jlayton@poochiereds.net>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>