Support netstat

Support for the netstat tool

On ubuntu:
```
~$ docker run --runtime=gvisor --rm -ti ubuntu su -c "apt update && apt install net-tools && netstat"
...
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags Type State I-Node Path
```

On alpine:
```
~$ docker run --runtime=gvisor --rm -ti alpine netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
netstat: /proc/net/raw: No such file or directory
netstat: /proc/net/raw6: No such file or directory
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags Type State I-Node Path
```