encapsulate a frame using this Secure Association

def encap(self, pkt):
        """encapsulate a frame using this Secure Association"""
        if pkt.name != Ether().name:
            raise TypeError('cannot encapsulate packet in MACsec, must be Ethernet')  # noqa: E501
        hdr = copy.deepcopy(pkt)
        payload = hdr.payload
        del hdr.payload
        tag = MACsec(sci=self.sci, an=self.an,
                     SC=self.send_sci,
                     E=self.e_bit(), C=self.c_bit(),
                     shortlen=MACsecSA.shortlen(pkt),
                     pn=(self.pn & 0xFFFFFFFF), type=pkt.type)
        hdr.type = ETH_P_MACSEC
        return hdr / tag / payload