BUG/MEDIUM: quic: keylog callback not called (USE_OPENSSL_COMPAT)

BUG/MEDIUM: quic: keylog callback not called (USE_OPENSSL_COMPAT)

This bug impacts only the QUIC OpenSSL compatibility module (USE_QUIC_OPENSSL_COMPAT)
and it was introduced by this commit:

    BUG/MINOR: quic: Wrong keylog callback setting.

quic_tls_compat_keylog_callback() callback was no more set when the SSL keylog was
enabled by tune.ssl.keylog setting. This is the callback which sets the TLS secrets
into haproxy.

Set it again when the SSL keylog is not enabled by configuration.

Thank you to @Greg57070 for having reported this issue in GH #2412.

Must be backported as far as 2.8.