ipfixprobe: MSS fix

[hulakmat]

Parser is parsing MSS value as 4 byte variable instead of 2 bytes. MSS option has 4 bytes: 1B kind, 1B length and only 2B value. In current condition MSS value generated by ipfixprobe is incorrect and MSS field size is too big.

Parser fix should be easy, ipfixprobe fields change needs revision.