Update p0f to version 3.0.7b, add test

- Update p0f to version 3.0.7b.
- Add a simple test in which p0f reads a pcap file.

In the test we write a simple binary pcap file (included in the recipe base64-encoded) and then attempt to read the file with p0f.

That would be way cleaner, but that pcap only contains an Ethernet frame.  p0f fingerprints off of data in the TCP and IP headers found in a packet.

Looks like only a couple formula are that fixture, so I'd imagine it would be pretty safe to replace it with a more useful pcap.