fae5282c82
Before b59b3d4 the migration code checked that service level controller
is on v2 version before migration and the check also implicitly checked
that _sl_data_accessor field is already initialized, but now that the
check is gone the migration can start before service level controller is
fully initialized. Re add the check, but to a different place.
Fixes https://scylladb.atlassian.net/browse/SCYLLADB-1049
Closes scylladb/scylladb#29021