smoketest: T5467: verify OSPF(v3) interface removal in VRF context

Testcases after the bugfix in commit 011697508 ("T5467: removing ospf(v3) or
isis interface in VRF context did not clear FRR config").

For ISIS change in the tests - do not run self_commit() in a for loop if not
really necessary, this will slow down the tests.