Make `PortList.Pop()` thread-safe (#11799)
Make `PortList.Pop()` thread-safe (#11799)

* Make `PortList.Pop()` thread-safe

* Store a `[]int` instead of `[]string` in `PortList`
gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport