ZeroNet reports IPv6 UDP Port open in UI, but log repors ipv6: False, other tools says it is closed

### Step 1: Please describe your environment

* ZeroNet version:

* Operating system: Debian GNU/Linux 9 (stretch)
* Web browser: all
* Tor status: always disabled
* Opened port: no
* Special configuration: Active wireguard VPN connection with IPv6 support via http://mullvad.net

### Step 2: Describe the problem:
ZeroNet reports IPv6 UDP Port open but nmap says it is closed

Recheck is consistent..

ZeroNet's log reports it could not open the port:
```bash
[12:12:21] PeerPortchecker Checking port 26552 (ipv6) using checkMyaddr result: {'ip': 'xxx.xx.xxx.xxx', 'opened': False} in 1.198s
[12:12:21] PeerPortchecker Checking port 26552 (ipv4) using checkPortchecker result: {'ip': 'xxx.xx.xxx.xxx', 'opened': False} in 1.615s
[12:12:21] PeerPortchecker Trying to open port using UpnpPunch...
[12:12:31] ConnServer Server port opened ipv4: False, ipv6: False
```

Note: I ran `nmap` from the same host running with the active wireguard vpn and zeronet client. Various IPv6 port scan external web sites did not find the open port, although I'm not sure they checked UDP and IPv6 so if you can recommend a site to try let me know.

#### Steps to reproduce:

1. start wireguard vpn with ipv6 support via http://mullvad.net
2. start zeronet
3. run nmap to check port

#### Observed Results:

```bash
$ sudo nmap -sU -6 -p 26552 xxxx:xxxx:x:xxxx::xxxx

Starting Nmap 7.40 ( https://nmap.org ) at 2019-09-05 06:50 CDT
Nmap scan report for xxxx:xxxx:x:xxxx::xxxx
Host is up (0.12s latency).
PORT STATE SERVICE
26552/udp closed unknown
```

Reproduce the IPv6 UDP port check with the WireGuard setup and compare the UI result with the log output. Start by tracing the named PeerPortchecker and ConnServer entries, including checkMyaddr, checkPortchecker, and UpnpPunch. Done means the UI consistently reflects whether the IPv6 port is actually open.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.