You can explicitly to it to open in direction mode with an f=d
parameter. With that set and no start address, it should use the device's current location. So more like this:
"https://maps.google.com/maps?f=d&daddr=berlin"
Note: This doesn't work in a browser; it opens the directions page with a blank field for start. Used in an intent sent to the native maps application, it works correctly(at least on my 4.2.2 gNex).