MDEV-13451 Assertion `!recv_no_ibuf_operations' failed in ibuf_page_low()

During InnoDB startup, change buffer merge operations are prohibited
before recv_apply_hashed_log_recs(true), which performs the last phase
of redo log apply. Before this call, ibuf_init_at_db_start() would be
invoked, and it could trigger the debug assertion.

ibuf_init_at_db_start(): Do not declare the mini-transaction as
"inside change buffer", because nothing is being written in the
mini-transaction. The purpose of this function is only to initialize
the memory data structures from the persistent data structures.

storage/innobase/ibuf/ibuf0ibuf.cc

@@ -534,7 +534,6 @@ ibuf_init_at_db_start(void)
 
 	fseg_n_reserved_pages(header_page + IBUF_HEADER + IBUF_TREE_SEG_HEADER,
 			      &n_used, &mtr);
-	ibuf_enter(&mtr);
 
 	ut_ad(n_used >= 2);
 
@@ -556,7 +555,7 @@ ibuf_init_at_db_start(void)
 	mutex_exit(&ibuf_mutex);
 
 	ibuf->empty = page_is_empty(root);
-	ibuf_mtr_commit(&mtr);
+	mtr.commit();
 
 	ibuf->index = dict_mem_index_create(
 		"innodb_change_buffer", "CLUST_IND",