Fix: Use /128 for IPv6 prefix in ospf.areas integration test

This change accomodates devices from vendors that can correctly
implement the OSPFv3 RFC.

Author: ipspace

tests/integration/ospf/ospfv3/40-area-parameters.yml

@@ -10,6 +10,7 @@ message: |
 defaults.sources.extra: [ ../../wait_times.yml ]
 plugin: [ ospf.areas ]
 module: [ ospf ]
+addressing.loopback.prefix6: 128
 
 ospf.areas:
 # Stub areas -- totally stubby one, and one with default cost