Build the Key Data Encapsulation for GTK
        KeyID: 0
        Ref: 802.11i p81

def build_GTK_KDE(self):
        """Build the Key Data Encapsulation for GTK
        KeyID: 0
        Ref: 802.11i p81
        """
        return b''.join([
            b'\xdd',  # Type KDE
            chb(len(self.gtk_full) + 6),
            b'\x00\x0f\xac',  # OUI
            b'\x01',  # GTK KDE
            b'\x00\x00',  # KeyID - Tx - Reserved x2
            self.gtk_full,
        ])