Something has to so we can have udev rules rely on this. Right now the ID_BUS
setting is inconsistent: usb is set, ata and pci are set, bluetooth is not
set, rmi is too new to be featured.
70-mouse even relied on bluetooth even though it was never set
Commits 5e9eb156c and 32567f8 introduced persistent symlinks for input devices
with more than one interface. However, this does not ensure stability for the
"default" interface, i. e. with interface number 00 or a nonexisting one. If a
device with a higher interface number appears first, it'll claim the symlink
name without an interface number, and the "interface 00" device won't get any.
Fix this by creating the default symlink only for interface 00 or a nonexisting
one, so that we properly partition the two cases over the two rules.
https://launchpad.net/bugs/1057824