nshlib: Fix stack-buffer-overflow of nsh_redirect()

Board/Config/Command
  sim:nsh
  cat < /etc/init.d/rc.sysinit

Problem
  The NSH hangs after exec the test command.
  `nsh_redirect()` needs to save three fd but array length is only two, stack buffer overflowed!

Related: #2469

Signed-off-by: wangjianyu3 <[email protected]>

Author: JianyuWang0623

nshlib/nsh_console.h

@@ -71,7 +71,7 @@
  * See struct serialsave_s in nsh_console.c
  */
 
-#define SAVE_SIZE (2 * sizeof(int))
+#define SAVE_SIZE (3 * sizeof(int))
 
 /* Are we using the NuttX console for I/O?  Or some other character device? */