Add luatc binding

[sneaky-potato]

Testing steps:

1. Run TC Lua script in softirq (tc.lua)

local tc     = require("tc")
local action = require("linux.tc")

local function filter_sni(ctx)
	local skb = ctx:skb()
	print(string.format("[tc] skb_len: %d", #skb))
	ctx:action(action.ACT_OK)
end

tc.attach(filter_sni)

2. Create a classifier eBPF prgram (tc.bpf.c)

#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

extern int bpf_luatc_run(char *key, size_t key__sz, struct __sk_buff *tc_ctx) __ksym;

static char runtime[] = "examples/filter/tc";

int const TC_ACT_OK = 0;

SEC("classifier")
int filter_https(struct __sk_buff *tc_ctx)
{
	int action = bpf_luatc_run(runtime, sizeof(runtime), tc_ctx);
	return action < 0 ? TC_ACT_OK : action;
}

char _license[] SEC("license") = "Dual MIT/GPL";

3. Attach the compiler eBPF program to docker bridge

tc qdisc del dev docker0 clsact 2>/dev/null
tc qdisc add dev docker0 clsact

tc filter add dev docker0 egress \
    bpf da obj examples/filter/tc.bpf.o sec classifier

4. Generate traffic with docker

sudo docker run --rm alpine/curl http://localhost:8080