generic/423: statx mask of the reference file is different from the original file

generic/423: statx mask of the reference file is different from the original file

When running xfstests generic/423 to test system call statx() on
hard link files of NFS, it fails.  error message:

[!] attr 'stx_mask' differs from ref file, 7ff != e0

The values of parameter "mask" between the original file and the
reference file are different.  One is STATX_ALL;
The other is STATX_ATIME | STATX_BTIME | STATX_CTIME | STATX_MTIME.

Modify the function get_reference() to pass the "mask" in, and
change STATX_ATIME | STATX_BTIME | STATX_CTIME | STATX_MTIME to
"mask".

Signed-off-by: Cui Yue <cuiyue-fnst@cn.fujitsu.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>