This also includes a switch to tty refcounting. It makes sure, the
code no longer can access a freed TTY struct.

Sometimes the only thing needed is to pass tty down to the callies.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Samuel Ortiz <samuel@sortiz.org>
Cc: netdev@vger.kernel.org
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>