add ipv6 loopback example (#2223)
add ipv6 loopback example (#2223)


johnbelamaric/coredns,chrisohaver/coredns,jremond/coredns,jremond/coredns,miekg/coredns,johnbelamaric/coredns,ii/coredns,miekg/coredns,yongtang/coredns,coredns/coredns,ii/coredns