Automatically apply configuration changes in service

[julian-klode]

Currently the service needs to be restarted manually if the configuration was changed or the host files were refreshed. We should make that more automatic.

DNS server changes

As we re-route the DNS servers currently, we need to restart the service. It might make sense to use to use "virtual" IP addresses again, and then map them on demand instead of overriding routes for the existing servers. This also has the effect of enabling non-DNS packets for those servers again. One disadvantage is that Android might choose to use a non-VPN server under very high latency situations.

Host file changes

Instead of reading all host files into one set, we can read them into multiple sets in threads, and then combine them, and use an atomic reference in the VPN thread. We could also have a queue of changes to be done against the current set, and apply them after poll() returns, but merging in the VPN thread might be too slow.

[julian-klode]

Part of this (host file changes) should go into 0.4

[julian-klode]

Moving to 0.5. It's quite a bit of rework, and I want to get the IPv6 support and user interface tweaks out now, and not mix them with other changes that might potentially break stuff.

[julian-klode]

Refreshing host files now updates the running service automatically in master!