udev: update net_id comments

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udev: persistent naming - we cannot use virtio numbers as they are not stable

This reverts commit 8741f2defaf26aafe5ee0fd29954cfdf84ee519c: 'Add virtio-blk support to path_id' and
commit e3d563346c4237af23335cc6904e0662efdf62ad: 'udev: net_id - handle virtio buses'.

Distros may want to take note of this, as it changes behavior.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>