Add support for NAT-PMP

[samvv]

This pull request continues the conversation in #142 and adds support for NAT-PMP.

Some remarks:

• The ports are written to /config/protonvpn-port-tcp.txt and /config/protonvpn-port-udp.txt inside the Docker container
• Nothing has been documented in the README
• Before starting the natpmpc update loop, I manually try to connect one time with TCP and UDP and only signal connection successful if these commands succeed.

I tested this using Docker and it works. Example Docker config:

protonwire:
  container_name: protonwire
  # Use semver tags or sha256 hashes of manifests.
  # using latest tag can lead to issues when used with
  # automatic image updaters like watchtower/podman.
  image: ghcr.io/tprasadtp/protonwire:dev
  init: true
  environment:
    # Quote this value as server name can contain '#'.
    PROTONVPN_SERVER: "NL#12"
    # Set this to 1 to show debug logs for issue forms.
    DEBUG: "1"
    # Set this to 0 to disable kill-switch.
    KILL_SWITCH: "1"
    # Enable port forwarding
    NATPMP: "1"
  # NET_ADMIN capability is mandatory!
  cap_add:
  - NET_ADMIN
  # sysctl net.ipv4.conf.all.rp_filter is mandatory!
  # net.ipv6.conf.all.disable_ipv6 disables IPv6 as protonVPN does not support IPv6.
  # 'net.*' sysctls are not required on application containers,
  # as they share network stack with protonwire container.
  sysctls:
    net.ipv4.conf.all.rp_filter: 2
    net.ipv6.conf.all.disable_ipv6: 1
  volumes:
    - type: tmpfs
      target: /tmp
    - type: bind
      source: protonvpn.key
      target: /etc/protonwire/protonvpn-private-key
      read_only: true
    - type: bind
      source: protonvpn-port-tcp.txt
      target: /config/protonvpn-port-tcp.txt
    - type: bind
      source: protonvpn-port-udp.txt
      target: /config/protonvpn-port-udp.txt

Important

Make sure to touch protonvpn-port-tcp.txt and protonvpn-port-udp.txt before starting the containeer or Docker will make it a directory and it wont work.

Let me know what you think!

[samvv]

I've just noticed that NAT-PMP should work out of the box but that I have some issue in my setup. Closing this pull request for now.

Edit: I'm actually not sure about this. Will re-open if I know more.

[samvv]

Ok so from what I can understand libtorrent fails to execute its built-in NAT-PMP because there's no default route for 10.2.0.2. Adding the route manually only made things worse.

Therefore this pull request actually serves as a workaround until arvidn/libtorrent#7890 is accepted.