Node announces wrong public port

#### Version information:
go-ipfs version: 0.5.0-36789ea
Repo version: 9
System version: amd64/linux
Golang version: go1.13.10

running the latest docker image (ipfs/go-ipfs latest 8096fbc6044b) in docker 19.03.12 swarm mode on amd64

#### Description:

The announced public port is incorrect. The node correctly detects the public IP (which changes daily), but adds a made-up port that can not be used to connect.

Config:
```json
"Swarm": [
"/ip4/0.0.0.0/tcp/9010",
"/ip6/::/tcp/9010"
]
```

Router: forwarded public 9010 -> host 9010
Docker service: host 9010 -> container 9010

UPnP is disabled on the router

But advertised addresses are:
```
/ip4/127.0.0.1/tcp/9010/p2p/...
/ip4/172.18.0.21/tcp/9010/p2p/...
/ip4//tcp/1056/p2p/...
```

Expected behavior: advertise port 9010, which is open from the public and works together with the correctly found public ip.

I don't know where the node got that 1056, it's not a forwarded port, nor is it mentioned anywhere in the config.