test: ssl: Enable client authentication in handshake state tests

The endpoint initialization function was setting up
a certificate but the client certificate was not
used because client authentication was not enabled
(not enabled in the default SSL server configuration).

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

tests/suites/test_suite_ssl.function

@@ -967,6 +967,8 @@ int mbedtls_endpoint_init( mbedtls_endpoint *ep, int endpoint_type, int pk_alg,
     if( group_list != NULL )
         mbedtls_ssl_conf_groups( &(ep->conf), group_list );
 
+    mbedtls_ssl_conf_authmode( &( ep->conf ), MBEDTLS_SSL_VERIFY_REQUIRED );
+
     ret = mbedtls_ssl_setup( &( ep->ssl ), &( ep->conf ) );
     TEST_ASSERT( ret == 0 );