Most of patch originally from JD <john.duncan@oracle.com>

  Modify Ndb layers in 8.0+ to store and transfer longer opaque metadata
  in Ndb table definitions using a new key (MysqlDictMetadata) rather than
  changing the definition of the existing key (FrmData).

  This avoids breaking compatibility with existing Ndb versions which require
  that the FrmData keyed data is no longer than 6000 bytes to be able to
  parse a table definition.

  Being unable to parse a table definition affects cross version Backup
  and Restore, which is part of cross version Replication, as well as
  data node recovery code etc.

  Existing versions of Ndb will ignore any new key which they do not
  know, and so will ignore the longer metadata in any table definition they
  come across.  This means that longer metadata will be discarded, but
  that the tables can still be opened and operated on from the Ndb
  level.

  As a result, tables should not be created/altered by a new version API
  until all data nodes are upgraded to support the new key, as their
  opaque metadata will be discarded by the old datanodes.

  Reviewed-by : Magnus Blaudd <magnus.blaudd@oracle.com>