Decoded IPv6 packet (RFC 8200) — fixed header fields and the raw remainder of the packet.
sourceAddress / destinationAddress are 16-byte slices. payload's
length is always payloadLength bytes after decoding, and — because this
package does not parse extension headers — includes any extension
headers present, followed by the upper-layer data.
versionClassFlow: { version: number; trafficClass: number; flowLabel: number; }
payloadLength: number
nextHeader: number
hopLimit: number