Add the DNS server address to the filtering log

[ameshkov]

The problem is that users cannot check if the DNS request was made to the configured upstream, or to the fallback server.

[admitrevskiy]

Resolved.

Testing instructions for QA:
-Reinstall AG
-Enable DNS module
-Serf the web
-Go to the Filtering Log -> select any processed event
-You will see DNS Upstream in the event details screen

[TheHasagi]

Not solved.

[admitrevskiy]

Done.
@TheHasagi please check it in the next build.