tty: Don't change receive_room for ioctl(TIOCSETD)

tty_set_ldisc() is guaranteed exclusive use of the line discipline
by tty_ldisc_lock_pair_timeout(); shutting off input by resetting
receive_room is unnecessary.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_ldisc.c

@@ -540,9 +540,6 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 		return 0;
 	}
 
-	/* FIXME: why 'shutoff' input if the ldisc is locked? */
-	tty->receive_room = 0;
-
 	old_ldisc = tty->ldisc;
 	tty_lock(tty);