make tty helper functions extern

make tty helper functions extern

- lxc_console_cb_tty_stdin()
- lxc_console_cb_tty_master()
- lxc_setup_tios(int fd, struct termios *oldtios);
- lxc_console_winsz(int srcfd, int dstfd);
- lxc_console_cb_sigwinch_fd(int fd, uint32_t events, void *cbdata,
	struct lxc_epoll_descr *descr);
- lxc_tty_state *lxc_console_sigwinch_init(int srcfd, int dstfd);
- lxc_console_sigwinch_fini(struct lxc_tty_state *ts);

We can make use these functions in other modules.

Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>