The links where added to the socket one after the other. However,
the virtual socket had a link limit of 1, so whenever a new link was
added, the previously added one was removed.
There is not really a reason for why the link limit should be 1 instead
of something higher. I'm setting it to the max value: `0xFFF`.
I'm also setting the `input_link_limit` to that value. Blender does not
need this currently, but addons might have input sockets that allow
more than one incident link.
e699546bde