Allow monitoring internal states of einat eBPF programs

[EHfive]

• [ ] Provide some IPC mechanism to interact with einat daemon, it could be D-Bus, RPC or custom protocol on plain unix socket.
• [ ] Allow dumping formatted NAT records from einat eBPF maps
• [ ] Log structured NAT operations and errors to user space via BPF perf event or BPF ring buffer. This is questionable as it would increase complexity of eBPF programs and is only useful for debugging, and we already have unstructured printk logging.