frp 不能远程访问小米路由器页面

之前一直访问不了，也没有细究，以为是 frp 的问题。昨晚测试了一下，小米路由器严格检查 http 请求的 HOST 字段，如果是非局域网内的机器，就直接不响应了，或者响应重定向。

```
root@OpenWrt:~# curl -H "Host: baidu.com:123" 192.168.50.1 -v
> GET / HTTP/1.1
> Host: baidu.com:123
> User-Agent: curl/7.77.0
> Accept: */*
>

直接卡住了……

root@OpenWrt:~# curl -H "Host: 192.168.50.3" 192.168.50.1 -v
> GET / HTTP/1.1
> Host: 192.168.50.3
> User-Agent: curl/7.77.0
> Accept: */*
>
< HTTP/1.1 502 Bad Gateway
< Server: nginx/1.12.2
< Date: Wed, 01 Dec 2021 04:50:45 GMT
< Content-Type: text/html; charset=UTF-8
< Content-Length: 173
< Connection: close

root@OpenWrt:~# curl -H "Host: 192.168.50.2" 192.168.50.1 -v
> GET / HTTP/1.1
> Host: 192.168.50.2
> User-Agent: curl/7.77.0
> Accept: */*
>
< HTTP/1.1 403 Forbidden
< Server: nginx/1.12.2
< Date: Wed, 01 Dec 2021 04:54:37 GMT
< Content-Type: text/html; charset=UTF-8
< Transfer-Encoding: chunked
< Connection: close
< Cache-Control: no-cache
< Pragma: no-cache
< Expires: 0
<
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<head>
<meta charset="utf-8">
<title>OpenWrt - LuCI</title>