expose lock release error from iptables util

pkg/util/iptables/iptables.go

@@ -338,7 +338,7 @@ func (runner *runner) RestoreAll(data []byte, flush FlushFlag, counters RestoreC
 }
 
 type iptablesLocker interface {
-	Close()
+	Close() error
 }
 
 // restoreInternal is the shared part of Restore/RestoreAll
@@ -361,7 +361,11 @@ func (runner *runner) restoreInternal(args []string, data []byte, flush FlushFla
 		if err != nil {
 			return err
 		}
-		defer locker.Close()
+		defer func(locker iptablesLocker) {
+			if err := locker.Close(); err != nil {
+				glog.Errorf("Failed to close iptables locks: %v", err)
+			}
+		}(locker)
 	}
 
 	// run the command and return the output or an error including the output and error