Exception list for shadowserver

[kraigu]

Ideally, we could have a per-Shadowserver-report-type exclusion list, but I'd settle for an exclusion list for an IP.

For instance, a recursing DNS server will resolve domains for clients, and then appear to be the one generating the request for a malicious hostname. This will show up in the Shadowserver sinkhole report. If we could exclude a list of known recursing DNS servers from sinkhole reporting, my life would be much easier.