dh_kmgmt.c: Avoid expensive public key validation for known safe-prime groups

dh_kmgmt.c: Avoid expensive public key validation for known safe-prime groups

The partial validation is fully sufficient to check the key validity.

Thanks to Szilárd Pfeiffer for reporting the issue.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/25088)