If `select_from_ports` is evaluated lazily, we might miss a port during
the dependency check. A way to prevent this is to use the `:=` operator.
Fixesgenodelabs/genode#4618
The service is loaded dynamically VBoxSharedClipboard.so at runtime. The
VFS configuration mounts the shared object at /VBoxSharedClipboard.so as
the file is checked by contrib code before loading. An init
configuration in pkg/vbox6/runtime illustrates this and how to re-label
the VBoxSharedClipboard.so ROM to its real name
virtualbox6-sharedclipboard.lib.so.
