Add SSL presets.

No need to use a separate profile as in X.509, everything we need is already
in ssl_config. Just load appropriate values.
diff --git a/programs/x509/cert_app.c b/programs/x509/cert_app.c
index 7ae9015..d93aeba 100644
--- a/programs/x509/cert_app.c
+++ b/programs/x509/cert_app.c
@@ -399,7 +399,8 @@
          */
         if( ( ret = mbedtls_ssl_config_defaults( &conf,
                         MBEDTLS_SSL_IS_CLIENT,
-                        MBEDTLS_SSL_TRANSPORT_STREAM ) ) != 0 )
+                        MBEDTLS_SSL_TRANSPORT_STREAM,
+                        MBEDTLS_SSL_PRESET_DEFAULT ) ) != 0 )
         {
             mbedtls_printf( " failed\n  ! mbedtls_ssl_config_defaults returned %d\n\n", ret );
             goto exit;