MDEV-33361 Excessive delays in SET GLOBAL innodb_log_file_size

innodb_log_file_size_update(): Wait for buf_pool.done_flush_list
(that a flush batch has completed), not buf_pool.do_flush_list
(that the buf_flush_page_cleaner was woken up).

The condition variable buf_pool.done_flush_list is broadcast by the
buf_flush_page_cleaner() at the end of each batch, which is when the
log checkpoint can advance and where any log resizing may be completed.
The purpose of the condition variable buf_pool.do_flush_list is to
wake up the buf_flush_page_cleaner() thread because there is work to do.
If no thread is signaling that condition variable, this loop could
unnecessarily wait for up to 5 seconds too long for the log resizing
to be completed. By consuming signals it could also prevent the
buf_flush_page_cleaner() thread from waking up.

Tested by: Matthias Leich

storage/innobase/handler/ha_innodb.cc

@@ -18452,7 +18452,7 @@ static void innodb_log_file_size_update(THD *thd, st_mysql_sys_var*,
         const bool in_progress(buf_pool.get_oldest_modification(LSN_MAX) <
                                log_sys.resize_in_progress());
         if (in_progress)
-          my_cond_timedwait(&buf_pool.do_flush_list,
+          my_cond_timedwait(&buf_pool.done_flush_list,
                             &buf_pool.flush_list_mutex.m_mutex, &abstime);
         mysql_mutex_unlock(&buf_pool.flush_list_mutex);
         if (!log_sys.resize_in_progress())