avoid -Wfree-nonheap-object when buiding with gcc11

Signed-off-by: Shawn Carey <shawn.carey@netfoundry.io>
diff --git a/programs/test/udp_proxy.c b/programs/test/udp_proxy.c
index 66ead4a..b77994e 100644
--- a/programs/test/udp_proxy.c
+++ b/programs/test/udp_proxy.c
@@ -991,8 +991,8 @@
 
     for( delay_idx = 0; delay_idx < MAX_DELAYED_HS; delay_idx++ )
     {
-        mbedtls_free( opt.delay_cli + delay_idx );
-        mbedtls_free( opt.delay_srv + delay_idx );
+        mbedtls_free( opt.delay_cli[delay_idx] );
+        mbedtls_free( opt.delay_srv[delay_idx] );
     }
 
     mbedtls_net_free( &client_fd );