Suspected WriteOnlyTransaction leak in InterfaceStateChangeListener

As found in see NETVIRT-883 attachment, there appear to be a lot (write only) transactions that are opened in InterfaceStateChangeListener but apparently never closed:
org.opendaylight.netvirt.vpnmanager.InterfaceStateChangeListener.lambda$update$2(InterfaceStateChangeListener.java:220)
org.opendaylight.genius.datastoreutils.DataStoreJobCoordinator$MainTask.run(DataStoreJobCoordinator.java:285)

The first (today's) NETVIRT-883 attachment shows this many time over, but I suspect (haven't looked at the code) that they are actually all the same. With https://git.opendaylight.org/gerrit/#/c/62635/ they'll probably be filtered and smashed together into fewer in future reports - but we should try to fix them before so that they don't appear at all anymore!