mod_ssl: fix small memory leak in ssl_init_server_certs when ECDH is used.

SSL_CTX_set_tmp_ecdh increases reference count, so we have to call
EC_KEY_free, otherwise eckey will not be freed.

Backports: r1666363
Author: jkaluza
Reviewed by: rjung, ylavic, wrowe



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1682074 13f79535-47bb-0310-9956-ffa450edef68