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.
Signed-off-by: Roopesh Chander <roop@roopc.net>