add logs for veth creation

Change-Id: I429eb3e20e1681bc0809274990c147bf817c686b
diff --git a/core/io_worker.go b/core/io_worker.go
index 2657e4c..8524866 100644
--- a/core/io_worker.go
+++ b/core/io_worker.go
@@ -160,11 +160,13 @@
 	err1 := CreateVethPairs(inveth, outveth)
 	vethnames = append(vethnames, inveth)
 	if err1 != nil {
+		logger.Error("setupVethHandler failed", err1)
 		RemoveVeths(vethnames)
 		return nil, vethnames, err1
 	}
 	handler, err2 := getVethHandler(inveth)
 	if err2 != nil {
+		logger.Error("getVethHandler failed", err2)
 		RemoveVeths(vethnames)
 		return nil, vethnames, err2
 	}