Update schema to support parsing multiple layers of PCAP data

- Now parses parts of the link layer (ethernet) the network layer
  (IPv4, IPv6, ICMPv4) and the transport layer (TCP, UDP)
- Remove lldp.minimal capture since the new schema does not define lldp
- Add new IPv6 and ICMPv4 test captures
- Reformat PCAP schema for consistent indentation
- Using title case for element names