POX Controller fixes

It seems that POX controller has some bugs in its source code, which appears as errors in the output window like these lines:

INFO:packet:(ipv6) warning IP packet data incomplete (114 of 316)
INFO:packet:(dns) parsing questions: incomplete name
INFO:packet:(dhcp parse) warning DHCP packet data too short to parse header: data len 86

Following POX mailing list this can be fixed by editing the POX source code:

• add at line 244 in packet.dns:

    elif r.qtype == 28:
      assert isinstance(r.rddata, IPAddr6)
      return s + r.rddata.toRaw()

• change at line 435 in packet.dns:

  return IPAddr6.from_raw(l[beg_index : beg_index + dlen])

• add at line 521 in addresses.py:

  def toRaw (self):
    return self.raw

• change at line 4431 in openflow.libopenflow_01.py the value of OFP_DEFAULT_MISS_SEND_LEN to a bigger value (default is 128). This error happens because DHCP packets are truncated.