pack packets into large buffers when GSO is available

packet_handler_map.go

@@ -26,7 +26,9 @@ type connCapabilities struct {
 // rawConn is a connection that allow reading of a receivedPackeh.
 type rawConn interface {
 	ReadPacket() (*receivedPacket, error)
-	WritePacket(b []byte, addr net.Addr, oob []byte) (int, error)
+	// The size parameter is used for GSO.
+	// If GSO is not support, len(b) must be equal to size.
+	WritePacket(b []byte, size uint16, addr net.Addr, oob []byte) (int, error)
 	LocalAddr() net.Addr
 	SetReadDeadline(time.Time) error
 	io.Closer