vnet: fix format of deleted sw interfaces

As similar 535364e90459566b603661c3dbe360c72f59ad71 is
merged, printing possibly deleted interfaces by index
only in all the rest cases.

Type: improvement
Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>
Change-Id: I4fa58b382c0279ff893523ba0188fdb9b09e10af
diff --git a/src/vnet/dpo/interface_tx_dpo.c b/src/vnet/dpo/interface_tx_dpo.c
index 8705798..73f4e90 100644
--- a/src/vnet/dpo/interface_tx_dpo.c
+++ b/src/vnet/dpo/interface_tx_dpo.c
@@ -50,10 +50,7 @@
     CLIB_UNUSED(u32 indent) = va_arg(*ap, u32);
     vnet_main_t * vnm = vnet_get_main();
 
-    return (format(s, "%U-tx-dpo:",
-                   format_vnet_sw_interface_name,
-                   vnm,
-                   vnet_get_sw_interface(vnm, index)));
+    return format (s, "%U-tx-dpo:", format_vnet_sw_if_index_name, vnm, index);
 }
 
 static void