Allow disabling the min and max version

Reviewed-by: Viktor Dukhovni <openssl-users@dukhovni.org>

ssl/ssl_conf.c

diff --git a/ssl/ssl_conf.c b/ssl/ssl_conf.c
index 9529d30..2c40df1 100644
--- a/ssl/ssl_conf.c
+++ b/ssl/ssl_conf.c
@@ -332,6 +332,7 @@
         int version;
     };
     static const struct protocol_versions versions[] = {
+        {"None", 0},
         {"SSLv3", SSL3_VERSION},
         {"TLSv1", TLS1_VERSION},
         {"TLSv1.1", TLS1_1_VERSION},