Change the ecdhe curve configuration to the same way httpd is doing it.

Change the ecdhe curve configuration to the same way httpd is doing it.
This removes 'no ecdh' and renames 'ecdh curve auto' to ecdhe default.
The code uses now tls_config_set_ecdhecurves(3) so it is possible to
specify multiple curves now. If people specified curves in their config
they need to adjust their config now.
OK beck@