Support pcap-ng format

[salsferrazza]

Current pcap source input format type only supports classic PCAP and not PCAP-NG. This may entail a move to scapy from dpkt within the PcapFileMessageSource class.

[salsferrazza]

interim workaround is to run tshark -F pcap -r {pcapng file} -w {pcap file} on pcap ng file to produce legacy pcap format supported by txcode