If an application on the windows host uses rdesktops serial forwarding
the SERIAL_GET_PROPERTIES might get called and leads to an error returned.

This patch implements the ioctl without giving back any data, however no
error state is returned either.

Taken from:
http://sourceforge.net/p/rdesktop/bugs/372/#20fd

Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
--- rdesktop-1.8.3/serial.c.orig	2015-01-21 12:46:35.222209021 +0100
+++ rdesktop-1.8.3/serial.c	2015-01-21 12:52:53.739897582 +0100
@@ -935,6 +935,9 @@
 			DEBUG_SERIAL(("serial_ioctl -> SERIAL_SET_XON\n"));
 			tcflow(handle, TCION);
 			break;
+		case SERIAL_GET_PROPERTIES:
+			DEBUG_SERIAL(("serial_ioctl -> SERIAL_GET_PROPERTIES\n"));
+			break;
 		default:
 			unimpl("SERIAL IOCTL %d\n", request);
 			return RD_STATUS_INVALID_PARAMETER;