radvd (IPv6) is broken on systems with a USB ethernet interface
Bug 8429 addressed the regression that was introduced in 2.4.3 causing an error message such as "ioctl(SIOCGIFMEDIA) failed on ue0: Invalid argument" to be logged by radvd for ethernet interfaces (usb, bridge) which don't have SIOCGIFMEDIA properties.
I hoped the fix to bug 8429 which was originally reported by a user having problems with a bridge would also fix my USB ethernet problems (which I did mention in the bug discussion), but it did not. The fix corrected bridges but ignored USB ethernet devices.
As a result, in 2.4.4 I still cannot use IPv6.