In practices adds annotations in the new syntax: ``` +//go:build !linux // +build !linux ``` Fixes failing gotip PASSES='fmt' check: https://travis-ci.com/github/etcd-io/etcd/jobs/486453806
in v3.1.0 netutil couldn't get default interface for ipv6only hosts Fixes #7219
Fix https://github.com/coreos/etcd/issues/6841.