Possible to set OSPF backbone area as stub or nssa

[troglobit]

Current Behavior

Currently the YANG model approves of setting the backbone area as stub or nssa.

Expected Behavior

This is ignored by FRR, but I'd expect the YANG model to have a must expression to prevent changing the area type when the area is 0.0.0.0

Steps To Reproduce

No response

Additional information

A migration script should be added to drop any existing area type from area 0 for customers having this set today.