Content of /proc/net/tcp not what it is supposed to be

I've noticed something weird I couldn't reproduce on other docker images such as `ubuntu` or on a "real" distribution (i.e: not running in a container engine).

When I launch the command: `nc -l 9999`, I expect to see the in `/proc/net/tcp` something like this:

``` bash
0: 00000000:270F 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 132769 1 ffff880078ff4040 100 0 0 10 0
```

where the `00000000:270F` part corresponds to `:`. In this sample, I see `0.0.0.0:9999` (once converted to decimal). However on alpine docker I see random number for the port part instead of the 9999 I expect.

Here is a screenshot of my session: