The solution implemented in commit b8c331c causes the tunnel to
remain in 'Activating' state, without the ability to cancel that.
So, in this commit, instead of retrying DNS silently on
Activated-On-Demand tunnels, we fail the startTunnel() silently.
To summarize, if activate-on-demand is on:
- If started from the WireGuard app, show error using lastErrorFile
mechanism, suggesting a way to turn off Activate On Demand
- If not started from WireGuard app, don't call displayMessage()
(don't show error to user) and silently fail starting the tunnel
This combination causes iOS to keep trying to bring up the tunnel,
leading to a lot of displayMessage() alerts.
In this fix, if we get a DNS resolution error in an Activate On Demand
enabled tunnel, we silently retry 9 times (with a 4-second delay before
each retry) and then show the displayMessage() alert.
