node: Add ParamBegin/End

Use these commands to mark the begin and end of a series of Param
enumerations and configuration, like when doing format negotiation. The
idea is that the device can remain open while we do this.
Use this in adapter when negotiating a format.

src/pipewire/stream.c

@@ -410,6 +410,9 @@ static int impl_send_command(void *object, const struct spa_command *command)
 			stream_set_state(stream, PW_STREAM_STATE_STREAMING, NULL);
 		}
 		break;
+	case SPA_NODE_COMMAND_ParamBegin:
+	case SPA_NODE_COMMAND_ParamEnd:
+		break;
 	default:
 		pw_log_warn(NAME" %p: unhandled node command %d", stream,
 				SPA_NODE_COMMAND_ID(command));