Next level kill switch

[faern]

Should solve #522.

Adds an extra daemon setting called block_when_disconnected. This defaults to false and when false the app should work identical to how it works today. But when set to true it will block the firewall in in the same way it does when in blocked state, but also in the disconnected state.

This has the result that if a user explicitly clicks disconnect or exits the app GUI they will have all their internet access blocked until they connect the VPN tunnel again via the CLI or GUI.

Should add an extra level of safety for those afraid of accidentally clicking the disconnect button or those exiting the GUI and still expect to not leak for example.

Git checklist:

• Describe the change in CHANGELOG.md under the [Unreleased] header.
• Check that commits follow the Mullvad coding guidelines

---

This change is 

[faern]

I do not intend this PR to also add this to the GUI. I think we should add it as this PR proposes first and get that out and receive some feedback before we expose it in the GUI maybe.

[pronebird]

Reviewed 11 of 13 files at r1.
Reviewable status: 11 of 13 files reviewed, 1 unresolved discussion (waiting on @faern)

---

talpid-core/src/tunnel_state_machine/disconnected_state.rs, line 58 at r1 (raw file):

        match try_handle_event!(self, commands.poll()) {
            Ok(TunnelCommand::AllowLan(allow_lan)) => {
                let changed = shared_values.allow_lan != allow_lan;

You could avoid an extra boolean variable by moving this expression into if statement

if shared_values.allow_lan != allow_lan {
  shared_values.allow_lan = allow_lan;
  ...
}

[pronebird]

Reviewed 2 of 13 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @faern)

[pronebird]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @faern)

[pronebird]

Reviewable status: complete! all files reviewed, all discussions resolved

[faern]

Reviewable status: 12 of 13 files reviewed, all discussions resolved (waiting on @pronebird)

---

talpid-core/src/tunnel_state_machine/disconnected_state.rs, line 58 at r1 (raw file):

Previously, pronebird (Andrei Mihailov) wrote…

You could avoid an extra boolean variable by moving this expression into if statement

if shared_values.allow_lan != allow_lan {
  shared_values.allow_lan = allow_lan;
  ...
}

Ah. Of course. Well spotted. Fixed now.

[pronebird]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved