rs485pingpong: Set default tty settings, refs #39874

The rs485pingpon test tool uses partly the tty settings that are setup
prior to execution.
This might lead to problems when the tty is misconfigured.

Use the default tty settings from glibc instead.
This was inspired by "stty sane"

Change-Id: Ie1a5d69edddb967e4dc284a450e3195e53d6af3c

testcases/rs485pingpong/rs485pingpong.c

@@ -34,15 +34,19 @@
 /******************************************************************************/
 
 /* Standard Include Files */
-#include <stdio.h>
-#include <stdlib.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <termios.h>
-#include <time.h>
-#include <linux/serial.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <sys/ioctl.h>
+#include <sys/param.h>
+#include <time.h>
+#define TTYDEFCHARS
+#include <termios.h>
+#undef TTYDEFCHARS
 #include <asm/ioctls.h>
+#include <linux/serial.h>
 
 /* Harness Specific Include Files. */
 #include "old/test.h"
@@ -226,15 +230,21 @@ setup()
 	}
 
 	// Get old attribute
-	if (tcgetattr (fd, &termios)) {
+	if (tcgetattr(fd, &termios)) {
 		// This is not a serial device
 		tst_brkm(TBROK, cleanup,
 			"Can't read device configuration. Is this a serial device? \
 			Error:%d, %s\n", errno, strerror(errno));
 	}
 
+	termios.c_cflag = TTYDEF_CFLAG;
+	termios.c_iflag = TTYDEF_IFLAG;
+	termios.c_oflag = TTYDEF_OFLAG;
+	termios.c_lflag = TTYDEF_LFLAG;
+	memcpy(termios.c_cc, ttydefchars, MIN(sizeof(termios.c_cc), sizeof(ttydefchars))); // not 100% sure if this is sound and safe
+
 	// Set Speed into termios structure
-	if (cfsetospeed (&termios, baud)) {
+	if (cfsetspeed (&termios, baud)) {
 		tst_brkm(TBROK, cleanup,
 			"Can't set baud rate.  Error:%d, %s\n",
 			errno, strerror(errno));