gio: Mark the Seekable interface as consume-only
gio: Mark the Seekable interface as consume-only

The implementor class is not generated correctly, because of some
strangeness with the method names. And I don't think anyone would need
to implement it.

orion75/gtk-sharp,akrisiun/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,antoniusriha/gtk-sharp,orion75/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,antoniusriha/gtk-sharp,openmedicus/gtk-sharp,akrisiun/gtk-sharp,openmedicus/gtk-sharp,orion75/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,antoniusriha/gtk-sharp,antoniusriha/gtk-sharp,openmedicus/gtk-sharp,orion75/gtk-sharp,sillsdev/gtk-sharp,antoniusriha/gtk-sharp,orion75/gtk-sharp,Gankov/gtk-sharp,openmedicus/gtk-sharp,akrisiun/gtk-sharp,akrisiun/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,Gankov/gtk-sharp,akrisiun/gtk-sharp,Gankov/gtk-sharp