Create snappi-scapy utils

[chrispsommers]

It'd be nice to have a small library of utils to allow snappi and scapy to work together (if licensing issues are not an obstacle). For example, it'd be nice to be able to convert scapy packets to a flow packet spec and vice-versa. I found it useful to create packets in scapy to compare athena-captured packets against. It would be nice if I could have converted my transmit flow spec into scapy packets directly (e.g. I generated 255 packets with an increment pattern in the DIP, so give me those packets as a list of scapy packets which I can modify per my expected behavior in the DUT, then I can do a compare. FOr example of how I did it with scapy see https://github.com/chrispsommers/p4-guide/blob/c621ce0482f8c58b9bfddac545e997b473620f99/demo1-athena/ptf/demo1-snappi.py#L865.