READONLY: only send a control to schedule fast-vacuuming from child context iff we have a connection open to the main daemon

there are some child processes where we do not create a connection to the main daemon (switch_from_server_to_client()) because it is expensive to set up and we normally might not need to talk to the daemon at all via a domainsocket.
but we might want to still call to ctdb_ltdb_store() from such chil processes.

(This used to be ctdb commit 9e372a08c40087e6b5335aa298e94d88273566a5)

ctdb/client/ctdb_client.c

@@ -4123,7 +4123,9 @@ int switch_from_server_to_client(struct ctdb_context *ctdb, const char *fmt, ...
 		return -1;
 	}
 
-	 return 0;
+	ctdb->can_send_controls = true;
+
+	return 0;
 }
 
 /*

ctdb/common/ctdb_util.c

@@ -346,6 +346,7 @@ pid_t ctdb_fork(struct ctdb_context *ctdb)
 		if (ctdb->do_setsched) {
 			ctdb_restore_scheduler(ctdb);
 		}
+		ctdb->can_send_controls = false;
 	}
 	return pid;
 }

ctdb/include/ctdb_private.h

@@ -483,6 +483,9 @@ struct ctdb_context {
 
 	/* Used to defer db attach requests while in recovery mode */
 	struct ctdb_deferred_attach_context *deferred_attach;
+
+	/* if we are a child process, do we have a domain socket to send controls on */
+	bool can_send_controls;
 };
 
 struct ctdb_db_context {

ctdb/server/ctdb_vacuum.c

@@ -1560,8 +1560,16 @@ int32_t ctdb_local_schedule_for_deletion(struct ctdb_db_context *ctdb_db,
 		return ret;
 	}
 
-	/* child process: send the main daemon a control */
+	/* if we dont have a connection to the daemon we can not send
+	   a control. For example sometimes from update_record control child
+	   process.
+	*/
+	if (!ctdb_db->ctdb->can_send_controls) {
+		return -1;
+	}
 
+
+	/* child process: send the main daemon a control */
 	indata.dsize = offsetof(struct ctdb_control_schedule_for_deletion, key) + key.dsize;
 	indata.dptr = talloc_zero_array(ctdb_db, uint8_t, indata.dsize);
 	if (indata.dptr == NULL) {