USB: cdc-acm tell tty layer not to split things up.

It ensures that the tty level do not split
the send buffer into 2KB blocks.
Signed-off-by: NDavid Engraf <david.engraf@netcom.eu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/cdc-acm.c

@@ -489,6 +489,7 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
 	else
 		rv = 0;
 
+	set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
 	tty->driver_data = acm;
 	acm->tty = tty;