mod_ssl: follow up to r1868645.

mod_ssl: follow up to r1868645.

Restore ssl_callback_ServerNameIndication() even with OpenSSL 1.1.1+, which
depends on its return value (OK/NOACK), mainly on session resumption, for
SSL_get_servername() to consider or ignore the SNI (returning NULL thus
making SSLStrictSNIVHostCheck fail for possibly legitimate cases).

This means that init_vhost() should accurately return whether the SNI exists
in the configured vhosts, even when it's called multiple times (e.g. first
from ClientHello callback and then from SNI callback), so save that state in
sslconn->vhost_found and reuse it.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1868743 13f79535-47bb-0310-9956-ffa450edef68