T381399: Record and respect the `tunnel.anonymous` property re-added the tunnels.anonymous property with the expectation new imports would use boolean values. Older IPs will use NULL, as there is no way to retrieve that data but over time, assuming Spur documentation is correct, we should expect to see NULL value usage go down. If it goes down to 0, we should remove support for NULL. This would:

• Allow us to enforce the UNIQUE constraint on the property (this constraint doesn't work on NULL and will let any number of operators w/that value through)
• Clean up the code that checks for null values in order to prevent the insert
• Guarantee that every operator is unique so no actors get lost if IPs are every queried by that property