feat(proxyproto): add proxy protocol support (#7738)

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

core/dnsserver/server_tls.go

@@ -12,6 +12,7 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
 	"github.com/miekg/dns"
+	"github.com/pires/go-proxyproto"
 )
 
 // ServerTLS represents an instance of a TLS-over-DNS-server.
@@ -79,6 +80,9 @@ func (s *ServerTLS) Listen() (net.Listener, error) {
 	if err != nil {
 		return nil, err
 	}
+	if s.connPolicy != nil {
+		l = &proxyproto.Listener{Listener: l, ConnPolicy: s.connPolicy}
+	}
 	return l, nil
 }