Return 0 if no tap interfaces are ready

Otherwise, if tapcli-rx manages to make it into polled-mode, it will
never leave polled mode. This has been wrong since day 1, sometime in
early 2013.

Change-Id: I124e01a48db5abbc4eb5240c8d59f76dc562e9f2
Signed-off-by: Dave Barach <dave@barachs.net>

vnet/vnet/unix/tapcli.c

@@ -369,7 +369,7 @@ tapcli_rx (vlib_main_t * vm,
   }));
 
   if (vec_len (ready_interface_indices) == 0)
-    return 1;
+    return 0;
 
   for (i = 0; i < vec_len(ready_interface_indices); i++)
   {