tty: Document c_line == N_TTY initial condition

The line discipline id is stored in the tty's termios; document the
implicit initial value of N_TTY.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -123,7 +123,8 @@ struct ktermios tty_std_termios = {	/* for the benefit of tty drivers  */
 		   ECHOCTL | ECHOKE | IEXTEN,
 	.c_cc = INIT_C_CC,
 	.c_ispeed = 38400,
-	.c_ospeed = 38400
+	.c_ospeed = 38400,
+	/* .c_line = N_TTY, */
 };
 
 EXPORT_SYMBOL(tty_std_termios);