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>