MDEV-16457 mariabackup 10.2+ should default to innodb_checksum_algorithm=crc32

Since MariaDB Server 10.2.2 (and MySQL 5.7), the default value of
innodb_checksum_algorithm is crc32 (CRC-32C), not the inefficient "innodb"
checksum. Change Mariabackup to use the same default, so that checksum
validation (when using the default algorithm on the server) will take less
time during mariabackup --backup. Also, mariabackup --prepare should be
a little faster, and the server should read backups faster, because the
page checksums would only be validated against CRC-32C.

Author: dr-m

extra/mariabackup/xtrabackup.cc

@@ -1193,7 +1193,7 @@ struct my_option xb_server_options[] =
   "The algorithm InnoDB uses for page checksumming. [CRC32, STRICT_CRC32, "
    "INNODB, STRICT_INNODB, NONE, STRICT_NONE]", &srv_checksum_algorithm,
    &srv_checksum_algorithm, &innodb_checksum_algorithm_typelib, GET_ENUM,
-   REQUIRED_ARG, SRV_CHECKSUM_ALGORITHM_INNODB, 0, 0, 0, 0, 0},
+   REQUIRED_ARG, SRV_CHECKSUM_ALGORITHM_CRC32, 0, 0, 0, 0, 0},
 
   {"innodb_undo_directory", OPT_INNODB_UNDO_DIRECTORY,
    "Directory where undo tablespace files live, this path can be absolute.",