net/netaddr: start migrating to net/netip via new netaddr adapter package

Updates #5162

Change-Id: Id7bdec303b25471f69d542f8ce43805328d56c12
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/nettype/nettype.go

@@ -8,6 +8,7 @@ package nettype
 import (
 	"context"
 	"net"
+	"net/netip"
 )
 
 // PacketListener defines the ListenPacket method as implemented
@@ -16,6 +17,10 @@ type PacketListener interface {
 	ListenPacket(ctx context.Context, network, address string) (net.PacketConn, error)
 }
 
+type PacketListenerWithNetIP interface {
+	ListenPacket(ctx context.Context, network, address string) (PacketConn, error)
+}
+
 // Std implements PacketListener using the Go net package's ListenPacket func.
 type Std struct{}
 
@@ -23,3 +28,24 @@ func (Std) ListenPacket(ctx context.Context, network, address string) (net.Packe
 	var conf net.ListenConfig
 	return conf.ListenPacket(ctx, network, address)
 }
+
+type PacketConn interface {
+	net.PacketConn
+	WriteToUDPAddrPort([]byte, netip.AddrPort) (int, error)
+}
+
+func MakePacketListenerWithNetIP(ln PacketListener) PacketListenerWithNetIP {
+	return packetListenerAdapter{ln}
+}
+
+type packetListenerAdapter struct {
+	PacketListener
+}
+
+func (a packetListenerAdapter) ListenPacket(ctx context.Context, network, address string) (PacketConn, error) {
+	pc, err := a.PacketListener.ListenPacket(ctx, network, address)
+	if err != nil {
+		return nil, err
+	}
+	return pc.(PacketConn), nil
+}