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/x509/cert_app.c b/programs/x509/cert_app.c
index 0656ce7..cdd77f2 100644
--- a/programs/x509/cert_app.c
+++ b/programs/x509/cert_app.c
@@ -441,7 +441,14 @@
             goto ssl_exit;
         }
 
-        mbedtls_ssl_set_bio( &ssl, &server_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, &server_fd,
+                             mbedtls_net_send, mbedtls_net_recv, NULL );
+#else
+        mbedtls_ssl_set_bio_ctx( &ssl, &server_fd );
+#endif
 
         /*
          * 4. Handshake