Revert "component/mariadb: version up 10.2.6 (GA) in mariadb/mariarocks.cfg."

This reverts commit ae0fd674.

Because mysqlclient 1.3.10 cannot be built :

_mysql.c: In function '_mysql_ConnectionObject_ping':
_mysql.c:1911:41: error: 'MYSQL' has no member named 'reconnect'
  if ( reconnect != -1 ) self->connection.reconnect = reconnect;
                                         ^
error: Setup script exited with error: command 'gcc' failed with exit status 1

component/mariadb/mariadb_10.2.6_MDEV-12281.patch

-diff -ur storage/xtradb/dict/dict0stats.cc storage/xtradb/dict/dict0stats.cc
---- storage/xtradb/dict/dict0stats.cc	2017-05-02 07:13:52.000000000 +0200
-+++ storage/xtradb/dict/dict0stats.cc	2017-05-09 09:53:50.174738190 +0200
-@@ -1168,10 +1168,10 @@
- 		leaf-level delete marks because delete marks on
- 		non-leaf level do not make sense. */
- 
--		if (level == 0 && srv_stats_include_delete_marked? 0:
-+		if (level == 0 && (srv_stats_include_delete_marked? 0:
- 		    rec_get_deleted_flag(
- 			    rec,
--			    page_is_comp(btr_pcur_get_page(&pcur)))) {
-+			    page_is_comp(btr_pcur_get_page(&pcur))))) {
- 
- 			if (rec_is_last_on_page
- 			    && !prev_rec_is_copied

component/mariadb/mariarocks.cfg

 [mariadb]
-url = https://downloads.mariadb.com/MariaDB/mariadb-10.2.6/source/mariadb-10.2.6.tar.gz
-md5sum = 3d454cdadbd3208e1c9c23e5338a62b0
+url = https://downloads.mariadb.com/MariaDB/mariadb-10.2.5/source/mariadb-10.2.5.tar.gz
+md5sum = 16fb01bb375c8d8a91a9ecf491397d51
 stable-patches =
-  ${:_profile_base_location_}/mariadb_10.2.6_MDEV-12281.patch#9e94e4f41559ae4f16db6fc0379a6fba
+pre-configure =
+  sed -i -e '/(rc == -1 || errno == EINTR)/s/||/\&\&/' libmariadb/plugins/pvio/pvio_socket.c
+  sed -i -e 's,set(SYSTEM_LIBS $${CMAKE_THREAD_LIBS_INIT}),set(SYSTEM_LIBS $${CMAKE_THREAD_LIBS_INIT} $${LIBRT}),' storage/rocksdb/build_rocksdb.cmake
 configure-options +=
   -DPLUGIN_DAEMON_EXAMPLE=NO
   -DPLUGIN_EXAMPLE=NO