[interface] Default to calling intf_restart() in response to intf_close()

If an object interface does not provide an intf_close() method, then
default to calling intf_restart().  This allows static objects to
safely ignore intf_close(), without needing to add code solely to
ensure that the interface gets unplugged.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/interface.c

  *
  */
 
+/**
+ * Close null interface
+ *
+ * @v intf		Null interface
+ * @v rc		Reason for close
+ */
+static void null_intf_close ( struct interface *intf __unused,
+			      int rc __unused ) {
+
+	/* Do nothing.  In particular, do not call intf_restart(),
+	 * since that would result in an infinite loop.
+	 */
+}
+
 /** Null interface operations */
-static struct interface_operation null_intf_op[] = {};
+static struct interface_operation null_intf_op[] = {
+	INTF_OP ( intf_close, struct interface *, null_intf_close ),
+};
 
 /** Null interface descriptor */
 struct interface_descriptor null_intf_desc =
 	if ( op ) {
 		op ( object, rc );
 	} else {
-		/* Default is to ignore intf_close() */
+		/* Default is to restart the interface */
+		intf_restart ( dest, rc );
 	}
 
 	intf_put ( dest );