The link I gave to Linx showed its recommended footprint for the PCB (page 35). It does not include the castellations. Instead, it has regular rectangular/square SMD pads. What you seem to show is the board outline of the device you are using, not its recommended footprint.
You could make specially shaped "pads" in Eagle with the semi-circular indentations, but why? The castellations might make soldering and routing more difficult.
Directly to your question, I have not seen castellated footprints in Eagle. If they exist, your most likely place to find them are on the Eagle site in the additional libraries section.
If you need to make it yourself, an easy way would be to copy the footprint for almost any 16-pin, 1.5 mm SMD device and modify it to the correct width. You can also click on the pads in the package editor and change the size to whatever you want. If you want to make your own castellated pads, I would do it in that editor. That will save having to draw the whole package and get spacings correct.
John