isdn: capi, remove optional tty ops

break_ctl and set_ldisc are optional tty_operations hooks. Given capi
does nothing useful in them, just remove these.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20210505091928.22010-33-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>