Fix API return code in case of error.

Change-Id: I22f866bacbc9c6e3abb0405f5c5a205910cec17b
Signed-off-by: Igor Mikhailov (imichail) <imichail@cisco.com>
diff --git a/src/plugins/abf/abf_itf_attach.c b/src/plugins/abf/abf_itf_attach.c
index 166ccec..151fb98 100644
--- a/src/plugins/abf/abf_itf_attach.c
+++ b/src/plugins/abf/abf_itf_attach.c
@@ -258,7 +258,7 @@
   aia = abf_itf_attach_db_find (policy_id, sw_if_index);
 
   if (NULL == aia)
-    return (VNET_API_ERROR_ENTRY_ALREADY_EXISTS);
+    return (VNET_API_ERROR_NO_SUCH_ENTRY);
 
   /*
    * first remove from the interface's vector