tty: Fix PPP hang under load

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/tty.h b/include/linux/tty.h
index f881697..bbbeaef 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -301,6 +301,7 @@
 #define TTY_PUSH 		6	/* n_tty private */
 #define TTY_CLOSING 		7	/* ->close() in progress */
 #define TTY_LDISC 		9	/* Line discipline attached */
+#define TTY_LDISC_CHANGING 	10	/* Line discipline changing */
 #define TTY_HW_COOK_OUT 	14	/* Hardware can do output cooking */
 #define TTY_HW_COOK_IN 		15	/* Hardware can do input cooking */
 #define TTY_PTY_LOCK 		16	/* pty private */