zfs: Revert "ZFS_IOC_COUNT_FILLED does unnecessary txg_wait_synced()"

This reverts commit 5198511.

It results in data corruption, see:
openzfs/zfs#14753

Sponsored by:	Rubicon Communications, LLC ("Netgate")

sys/contrib/openzfs/module/zfs/dnode.c

@@ -1764,29 +1764,20 @@ dnode_try_claim(objset_t *os, uint64_t object, int slots)
 }
 
 /*
- * Checks if the dnode might contain any uncommitted changes to data blocks.
- * Dirty metadata (e.g. bonus buffer) does not count.
+ * Checks if the dnode contains any uncommitted dirty records.
  */
 boolean_t
 dnode_is_dirty(dnode_t *dn)
 {
 	mutex_enter(&dn->dn_mtx);
+
 	for (int i = 0; i < TXG_SIZE; i++) {
-		list_t *list = &dn->dn_dirty_records[i];
-		for (dbuf_dirty_record_t *dr = list_head(list);
-		    dr != NULL; dr = list_next(list, dr)) {
-			if (dr->dr_dbuf == NULL ||
-			    (dr->dr_dbuf->db_blkid != DMU_BONUS_BLKID &&
-			    dr->dr_dbuf->db_blkid != DMU_SPILL_BLKID)) {
-				mutex_exit(&dn->dn_mtx);
-				return (B_TRUE);
-			}
-		}
-		if (dn->dn_free_ranges[i] != NULL) {
+		if (multilist_link_active(&dn->dn_dirty_link[i])) {
 			mutex_exit(&dn->dn_mtx);
 			return (B_TRUE);
 		}
 	}
+
 	mutex_exit(&dn->dn_mtx);
 
 	return (B_FALSE);
@@ -2650,9 +2641,7 @@ dnode_next_offset(dnode_t *dn, int flags, uint64_t *offset,
 		rw_enter(&dn->dn_struct_rwlock, RW_READER);
 
 	if (dn->dn_phys->dn_nlevels == 0) {
-		if (!(flags & DNODE_FIND_HOLE)) {
-			error = SET_ERROR(ESRCH);
-		}
+		error = SET_ERROR(ESRCH);
 		goto out;
 	}