You can run any program in container's namespace using nsenter utility.
$ docker inspect -f '{{.State.Pid}}' fs.neo.org
27242
$ sudo nsenter -t 27242 -n netstat -antp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.11:43783 0.0.0.0:* LISTEN 1376/dockerd
tcp6 0 0 :::443 :::* LISTEN 27242/nginx: master
tcp6 0 0 :::80 :::* LISTEN 27242/nginx: master