Check whitelists before checking DNS

This change is a slight performance improvement, as well as a bug fix for the case where an IP address is in the whitelist.  Basically, the whitelist should always be checked before any run of DNS queries, as there is nothing that uses this result other than the plugin.

The bug is that IP addresses in the whitelist were never checked if the forward DNS didn't point back to the IP address.  The performance improvement comes from not having to check DNS if there is already a whitelist rule for an IP, and perhaps not having to check forward DNS if there is an entry for the name in the whitelist.