nf-queue 0.1.0

# Netfilter Queue

A thin wrapper around `libmnl` for netfilter queue.

# Example
```rust
use crate::{CfgFlag, CmdType, CopyMode, MsgBuilder, SOCKET_BUFFER_SIZE, Socket, VerdictType};
use std::error::Error;

const QUEUE_NUM: u16 = 0;

fn main() -> Result<(), Box<dyn Error>> {
    let socket = Socket::new(0)?;

    let mut recv_buf = vec![0; 0xffff + (SOCKET_BUFFER_SIZE / 2)];
    let mut send_buf = vec![0; SOCKET_BUFFER_SIZE];

    let msg = MsgBuilder::new(&mut send_buf, QUEUE_NUM)
        .ack()
        .cfg()
        .cmd(CmdType::Bind)
        .params(0xffff, CopyMode::Packet)
        .queue_maxlen(1024)
        .flags(CfgFlag::FailOpen | CfgFlag::ConnTrack | CfgFlag::Gso)
        .build();

    socket.send(msg)?;
    socket.recv(&mut recv_buf)?; // ACK

    loop {
        let messages = socket.recv(&mut recv_buf)?;

        for msg in messages {
            let packet_msg = msg.as_packet_msg().unwrap();
            let packet_hdr = packet_msg.packet_hdr().unwrap();

            println!("{packet_msg:#?}");

            let verdict = MsgBuilder::new(&mut send_buf, QUEUE_NUM)
                .verdict()
                .verdict_hdr(packet_hdr.packet_id, VerdictType::Accept)
                .build();

            socket.send(verdict)?;
        }
    }
}
```