Sieve-tools: use 'mail' as module name in stead of the name of the command.

src/lib-sieve-tool/sieve-tool.c

@@ -200,7 +200,7 @@ struct sieve_instance *sieve_tool_init_finish
 			MAIL_STORAGE_SERVICE_FLAG_USERDB_LOOKUP;
 
 	memset(&service_input, 0, sizeof(service_input));
-	service_input.module = tool->name;
+	service_input.module = "mail";
 	service_input.service = tool->name;
 	service_input.username = username;