vfs_gpfs: handle EACCES when fetching DOS attributes from xattr

vfs_gpfs: handle EACCES when fetching DOS attributes from xattr

When trying to fetch the DOS attributes via gpfswrap_get_winattrs_path()
if the filesystem doesn't grant READ_ATTR to the file the function fails
with EACCESS.

But according to MS-FSA 2.1.5.1.2.1 "Algorithm to Check Access to an
Existing File" FILE_LIST_DIRECTORY on a directory implies
FILE_READ_ATTRIBUTES for directory entries.

So if the user can open the parent directory for reading this implies
FILE_LIST_DIRECTORY and we can safely call gpfswrap_get_winattrs_path()
with DAC_OVERRIDE_CAPABILITY.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12944

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Wed Aug  9 01:21:14 CEST 2017 on sn-devel-144