Fix the MAX_CURVELIST definition

The MAX_CURVELIST macro defines the total number of in-built SSL/TLS curves
that we support. However it has not been updated as new curves are added.

Fixes #5232

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/6065)