Fix SSL_CTX_get_{min,max}_proto_version integer conversion warning
Fix SSL_CTX_get_{min,max}_proto_version integer conversion warning

When using the SSL_CTX_get_min_min_version macro while compiling with
-Wall, my compiler rightfully complains about this construction:

warning: passing argument 3 of ‘SSL_CTX_ctrl’ makes integer from
pointer without a cast [-Wint-conversion]

These macro's should use 0, instead of NULL, for the third argument,
like most other SSL_CTX_ctrl 'get' wrappers do.

CLA: trivial
Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>

Reviewed-by: Matt Caswell <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@openssl.org>
Reviewed-by: Kurt Roeckx <bb87b47479d83cec3c76132206933257ded727b2@roeckx.be>
Reviewed-by: Ben Kaduk <b34e9dc3dd24827b45bb22e8b76cde1bcb413b0e@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/5099)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl