[PPP]: Fix ppp_async xon/xoff handling.

drivers/char/tty_io.c

@@ -611,6 +611,8 @@ void stop_tty(struct tty_struct *tty)
 		(tty->driver->stop)(tty);
 }
 
+EXPORT_SYMBOL(stop_tty);
+
 void start_tty(struct tty_struct *tty)
 {
 	if (!tty->stopped || tty->flow_stopped)
@@ -629,6 +631,8 @@ void start_tty(struct tty_struct *tty)
 	wake_up_interruptible(&tty->write_wait);
 }
 
+EXPORT_SYMBOL(start_tty);
+
 static ssize_t tty_read(struct file * file, char * buf, size_t count, 
 			loff_t *ppos)
 {

drivers/net/ppp_async.c

@@ -891,6 +891,11 @@ ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
 			process_input_packet(ap);
 		} else if (c == PPP_ESCAPE) {
 			ap->state |= SC_ESCAPE;
+		} else if (I_IXON(ap->tty)) {
+			if (c == START_CHAR(ap->tty))
+				start_tty(ap->tty);
+			else if (c == STOP_CHAR(ap->tty))
+				stop_tty(ap->tty);
 		}
 		/* otherwise it's a char in the recv ACCM */
 		++n;