Fixes: #18433 - Fix missing is_primary property on MACAddress model

[DanSheps]

Fixes: #18433 - Add missing is_primary property on MACAddress model

• Added missing is_primary property method on MACAddress model

[bctiemann]

I had is_primary on the model as a concrete field initially, then changed it to primary_for_interface field on the related model during development/review. I guess the template still had the vestigial mention. I'm not sure why we didn't put it back in as a property, but I seem to remember wanting to but there was some argument against it?

Approved for the moment, but there might be some discussion to be had.

[DanSheps]

I had is_primary on the model as a concrete field initially, then changed it to primary_for_interface field on the related model during development/review. I guess the template still had the vestigial mention. I'm not sure why we didn't put it back in as a property, but I seem to remember wanting to but there was some argument against it?

I think is_primary as a "Boolean" makes sense. If it was is_primary as the reverse relation it would be kind of weird IMO.

[bctiemann]

@DanSheps please fix merge conflict