Make parsing Trap PDU as optional

[paliwalashish]

Can make parsing Trap PDU as optional. Flume just need to carry the data as byte[], hence parsing here may not provide a lot of benefit. This may not be possible with snmp4j, but using raw (N)IO library like Apache MINA or Netty. I wrote something similar, which can be reused here.

There may be situations where parsing a PDU might be of help. My knowledge is a bit rusty, but do we receive Traps on TCP? I remember only UDP. If so, the we don't need to add TCP mapping.