Example apps: Don't use runtime IO config API if CBs are hardcoded

Multiple example applications still use mbedtls_ssl_set_bio() even
if the I/O callbacks are hardcoded. This commit fixes this.
diff --git a/programs/ssl/ssl_server.c b/programs/ssl/ssl_server.c
index 849c14d..bf502a5 100644
--- a/programs/ssl/ssl_server.c
+++ b/programs/ssl/ssl_server.c
@@ -265,7 +265,14 @@
         goto exit;
     }
 
-    mbedtls_ssl_set_bio( &ssl, &client_fd, mbedtls_net_send, mbedtls_net_recv, NULL );
+#if !defined(MBEDTLS_SSL_CONF_RECV) &&          \
+    !defined(MBEDTLS_SSL_CONF_SEND) &&          \
+    !defined(MBEDTLS_SSL_CONF_RECV_TIMEOUT)
+    mbedtls_ssl_set_bio( &ssl, &client_fd,
+                         mbedtls_net_send, mbedtls_net_recv, NULL );
+#else
+    mbedtls_ssl_set_bio_ctx( &ssl, &client_fd );
+#endif
 
     mbedtls_printf( " ok\n" );