Don't check IP addresses against non-IAP sources

[gwire]

Occasionally IAPs will block access by routing specific IP addresses to their blocking infrastructure, for example this recent block for 186.2.163.219 targeting sci-hub.

For IP-based lookups, the public DNS checks (OpenDNS, CloudFlare Family DNS) should be skipped and have a neutral "Not Applicable" result. Currently an IP address lookup will give "Address lookup failed".