Migration plugins registered under the ``neutron.ovn.db_migration``
entry point are plain callables (functions), not subclasses of
``BaseOvnDbSynchronizer``. The shared ``_load_drivers`` helper applies
an ``issubclass`` guard that is only valid for class-based sync plugins,
causing a ``TypeError`` when loading function-based migration plugins and
ultimately a ``NoMatches`` exception that aborts the OVS-to-OVN database
migration step.
Fix this by giving ``load_db_migration_drivers`` its own
``EnabledExtensionManager`` construction that skips the ``issubclass``
check and simply filters by driver name.
Closes-Bug: #2160210
Assisted-By: Claude Sonnet 4.6
Change-Id: I5c9b689558a9553ff6968868b43bf3d9239c92ad
Signed-off-by: Michal Nasiadka <mnasiadka@gmail.com>
Michal Nasiadka
c615e18da9