Replace handling of negative verification result with SSL_set_retry_verify()

Replace handling of negative verification result with SSL_set_retry_verify()

Provide a different mechanism to indicate that the application wants
to retry the verification. The negative result of the callback function
now indicates an error again.

Instead the SSL_set_retry_verify() can be called from the callback
to indicate that the handshake should be suspended.

Fixes #17568

Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17825)