ssl_util.c: log which threadid callback is in use

This should help during testing and debugging. Use APLOG_NOTICE for now,
until we fix PR60999, so that people can actually see the log message.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/trunk-openssl-threadid@1791847 13f79535-47bb-0310-9956-ffa450edef68