Support g_fifo_af_xon

libraries/base/ring/src/vhdl/ring_mux.vhd

@@ -46,6 +46,7 @@ ENTITY ring_mux IS
     g_use_empty         : BOOLEAN := TRUE;
     g_use_error         : BOOLEAN := TRUE;
     g_use_sync          : BOOLEAN := TRUE;
+    g_fifo_af_xon       : NATURAL := 0;  -- >=0, Nof words below max (full) at which fifo is considered almost full for snk_out.xon
     g_fifo_size         : t_natural_arr := array_init(1024, 2)  -- must match c_nof_input
   );
   PORT (
@@ -94,8 +95,8 @@ BEGIN
     g_use_in_channel    => TRUE,
     g_use_error         => g_use_error,
     g_use_sync          => g_use_sync,
+    g_fifo_af_xon       => g_fifo_af_xon,
     g_fifo_size         => g_fifo_size
-    
   )
   PORT MAP (
     rst => dp_rst,