<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _check_len(self, pkt):
 """Check for odd packet length and pad according to Cisco spec. This padding is only used for checksum computation. The original packet should not be altered."""

        if len(pkt) % 2:
            last_chr = pkt[-1]
            if last_chr <= b'\x80':
                return pkt[:-1] + b'\x00' + last_chr
            else:
                return pkt[:-1] + b'\xff' + chb(orb(last_chr) - 1)
        else:
            return pkt