Returns true if pkt is using SOMEIP-TP, else returns false.

def _is_tp(pkt):
        """Returns true if pkt is using SOMEIP-TP, else returns false."""

        tp = [SOMEIP.TYPE_TP_REQUEST, SOMEIP.TYPE_TP_REQUEST_NO_RET,
              SOMEIP.TYPE_TP_NOTIFICATION, SOMEIP.TYPE_TP_RESPONSE,
              SOMEIP.TYPE_TP_ERROR]
        if isinstance(pkt, Packet):
            return pkt.msg_type in tp
        else:
            return pkt[15] in tp