* NAT64 BPF implementation

This directory contains a BPF implementation of a stateless NAT64
implementation, like that performed by Tayga, but entirely in BPF.

Design:

- Global v6 /96 prefix defined as NAT64 prefix
- Each interface is assigned a v4 prefix for mapping v6 addresses
  - Install onlink v4 route for that prefix to make sure traffic goes out the interface

- Attach ingress and egress BPF programs to each interface
  - On ingress: match v6 packets with a NAT64 prefix destination; remap to v4
  - On egress: lookup v4 destination address; if it's in the configured NAT64 prefix, remap back to v6

- Some logic to dynamically assign v4 addresses each time a new v6 source is seen