(This is a release-blocker via #11811.)

This was broken by https://golang.org/cl/347010, which updated the vendored x/net.

This pulled in https://golang.org/cl/321869, which reverts a change to routing message alignment on FreeBSD. ("Empirically, freebsd-386 builders are observing 64-bit aligned routing messages.")

It appears that the alignment of routing messages depends on the syscall used to fetch them. The route.RIBTypeInterface constant in x/net is syscall.NET_RT_IFLIST, but the net package tries to call route.FetchRIB with syscall.NET_RT_IFLISTL.

Unfortunately route.FetchRIB(syscall.AF_UNSPEC, NET_RT_IFLISTL) returns bad data rather than an error. This then leads to the test in x/net/ipv6 attempting to listen on "0:fe:8000::%lo0" (note the erroneous leading "0:") and failing.

(Prior to https://golang.org/cl/347010, this test passed because we failed to parse any interfaces correctly, and therefore never even attempted to call net.ListenPacket.)

I think the right fix is probably to change the net package to stop trying to pass NET_RT_IFLISTL to route.ParseRIB, rather than the route.RIBTypeInterface constant.

Change https://golang.org/cl/353611 mentions this issue: net: don't use syscall.NET_RT_IFLISTL on FreeBSD