Turns out the RDB checksum in Redis 6.0 on bigendian is broken.
It always returned 0, so the RDB files are generated as if checksum is
disabled, and will be loaded ok on littleendian, and on bigendian.
But it'll not be able to load RDB files generated on littleendian or older versions.
Similarly DUMP and RESTORE will work on the same version (0==0),
but will be unable to exchange dump payloads with littleendian or old versions.
(cherry picked from commit a67621f495762dfe09f9a7e28d12b0729a7b0d12)
