Add IP/subnet to flags

[jsocol]

It would be valuable to turn on flags by internal IP or subnet. A comma-separated list of IP addresses with wild cards would be great.

[adamhaney]

I currently have a need to be able to enable/disable flags by IP/subnet as well as the logic NOT of an IP/subnet and would be interested in contributing this. Does anyone have any strong opinions on API/design and/or would project maintainers be open to merging such functionality if I were to write it? This is probably a question best answered by @clintonb.

[clintonb]

@adamhaney sorry for the delay. I have no strong opinions. I'll provide feedback on the PR.