Closes #9068: validate addresses assigned to interfaces

[decoupca]

Fixes: #9068

Disallows assigning a broadcast address or network ID to an interface.

[jeremystretch]

Thanks for taking this!

[kkthxbye-code]

Doing validation like this in the form has the side-effect of only applying to the UI. This is an issue with large parts of the netbox codebase, but I think we should try to avoid it if possible.

With the PR it is now possible to create 10.0.0.0/24 in the API and assign it to an interface. When editing the new IP in the UI and saving without changes it gets the validation error. Not sure what the right solution is. Either the validation logic has to be in both the model form and the serializer, or the validation needs to be done on the model.

@jeremystretch - Any input? I would classify this fix as being buggy, as it makes the UI and API behave differently.

[jeremystretch]

It's not perfect but it is inline with the existing validation logic. I'm happy to review any proposed improvements.