Add TCP to collector for IPFIX

[bitkeks]

In IPFIX, exporters and collectors can/should use TCP or SCTP for their connection instead of UDP. At least TCP should be added to the collector in this repo.

Related to #20 IPFIX

[mrx3000]

Any update on the implementation?

[bitkeks]

Not for public use yet. There's an experimental implementation with async for TCP, but it is not stable enough for usage. Guess the UDP implementation should just be ported for TCP sockets, with some overhead to track sessions.