smackcipso can't set CIPSO correctly, see the bug report:
        https://tizendev.org/bugs/browse/TDIS-3891

The reason is that upstream libsmack only use "smackfs/cipso2" long-label interface,
but the code's logical is still for orginal fixed length label.

Now update smack_cipso_apply() to support flexible label (<=256 including tailing '\0')

Signed-off-by: Passion,Zhao <passion.zhao@intel.com>