SSL_CONF_cmd: fix doc for NoRenegotiation

The option is a flag for Options, not a standalone setting.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8292)

(cherry picked from commit 4ac5e43d)