vfs_streams_xattr: Do not attempt to write empty attribute twice

vfs_streams_xattr: Do not attempt to write empty attribute twice

The create disposition FILE_OVERWRITE_IF is mapped to the flags
O_CREAT|O_TRUNC. In vfs_streams_xattr, this triggers two calls to
SMB_VFS_SETXATTR. The second can fail if O_EXCL is also set, resulting
in an unnecessary error.

Merge the identical code to handle O_CREAT and O_TRUNC to avoid setting
an empty attribute twice. Also add the flags parameter to the debug
message.

Signed-off-by: Christof Schmitt <christof.schmitt@us.ibm.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
(cherry picked from commit 4cd7e1d283f060e794023d5b0a48a7ec97d33820)

The last two patches address bug #9970 - Backport vfs_streams_xattr fixes to 4.0
and 4.1.

Autobuild-User(v4-0-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-0-test): Wed Jul  3 12:22:43 CEST 2013 on sn-devel-104