1) relax version check for restore block since no changes has happend since 5.1.6
   and improve error message on check failure
   
2) improve lcp/backup max write size...


storage/ndb/src/kernel/blocks/backup/BackupInit.cpp:
  Increase max write size to 256k (currently not configurable...)
storage/ndb/src/kernel/blocks/restore.cpp:
  Relax version check for restore block since no changes has happend since 5.1.6
storage/ndb/src/kernel/blocks/restore.hpp:
  Relax version check for restore block since no changes has happend since 5.1.6