mdev: do not follow symlinks in /sys (as was intended prior to rev 18811).

If this breaks things, please document why!
mdev,init: use shared code for fd sanitization

function                                             old     new   delta
bb_daemonize_or_rexec                                155     172     +17
mdev_main                                            500     505      +5
init_main                                            907     856     -51
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 22/-51)            Total: -29 bytes

1 files changed, 1 insertions, 14 deletions

diff --git a/init/init.c b/init/init.c
index 232896709..4b2bd9c77 100644
--- a/init/init.c
+++ b/init/init.c
@@ -221,20 +221,7 @@ static void console_init(void)
 	} else {
 		/* Make sure fd 0,1,2 are not closed
 		 * (so that they won't be used by future opens) */
-
-		/* bb_sanitize_stdio(); - WRONG.
-		 * It fails if "/dev/null" doesnt exist, and for init
-		 * this is a real possibility! Open code it instead. */
-
-		int fd = open(bb_dev_null, O_RDWR);
-		if (fd < 0) {
-			/* Give me _ANY_ open descriptor! */
-			fd = xopen("/", O_RDONLY); /* we don't believe this can fail */
-		}
-		while ((unsigned)fd < 2)
-			fd = dup(fd);
-		if (fd > 2)
-			close(fd);
+		bb_sanitize_stdio();
 	}
 
 	s = getenv("TERM");