Some background: This was found due to bad interactions with one of the few remaining Android common kernel networking patches. (The one that makes it possible for RA's to create routes in interface specific tables)
The cleanup portion of it scours all tables and deletes all relevant ADDRCONF routes, which in 5.2-rc1+ now includes ::1/128 and thus terribly breaks things (in the Android Kernel Networking tests). However, it *is* a userspace visible change in behaviour (since it's visible via the above /proc file), so one could argue for the above patch (or something similar). The Android patch *could* also probably be adjusted to handle this case (and thus prevent the breakage). It's not immediately clear to me what is the better approach as I'm not immediately certain what RTF_ADDRCONF truly means. However the in kernel header file comment does explicitly mention this being used to flag routes derived from RA's, and very clearly ::1/128 is not RA generated, so I *think* the correct fix is to return to the old way the kernel used to do things and not flag with ADDRCONF... Opinions?
