STRV_FOREACH_BACWARDS: start at the tail of the list

Otherwise, the user would have to manually initialize the pointer. Nobody currently uses this code,
so the change in behaviour sohuld be fine.
udev: move udev_rules_check_timestamp to shared

I want to use this from a bulitin in a subsequent patch.
udev-builtin: path_id - add support for bcma bus

This matches the bcma support in the network device naming.

Eventually wa want to make sure ID_PATH is equivalent to ID_NET_NAME_PATH,
so we never need to match on the latter.