TS_SSL_CLIENT_HELLO_HOOK is unavailable with BoringSSL

[maskit]

TS_SSL_CLIENT_HELLO_HOOK is not called if you use ATS with BoringSSL. This is because SSL_CTX_set_client_hello_cb is not available on BoringSSL. We might be able to use SSL_CTX_set_select_certificate_cb instead.

Autest tls_hooks16, 17 and 18 fail because of this.

[randall]

I believe this can be closed now. ATS now uses SSL_CTX_set_select_certificate_cb with BoringSSL (added in #8014)