mariadb: bump to 10.2.22

mariadb: bump to 10.2.22

From upstream release notes:

- Backport Information Schema CHECK_CONSTRAINTS Table.
- MDEV-17475: Maximum value of table_definition_cache is now 2097152.
- InnoDB ALTER TABLE fixes: MDEV-16499, MDEV-18186, MDEV-18237, MDEV-18222,
  MDEV-18256, MDEV-18016, MDEV-16849
- Mariabackup fixes: MDEV-18185, MDEV-18201, MDEV-18194
- Galera crash recovery fix: MDEV-15740
- Encryption fixes: MDEV-18129, MDEV-18183, MDEV-18279
- Fixes for the following security vulnerabilities:
  - CVE-2019-2510
  - CVE-2019-2537

OpenWrt notes:
- OpenSSL patch dropped as issue fixed upstream

Signed-off-by: Sebastian Kemper <redacted>