spice.proto: add @outvar markup
spice.proto: add @outvar markup

With this we can reference pointer member with no naming conflicts

fgouget/spice-protocol,vdiot/spice-protocol,vdiot/spice-protocol,fgouget/spice-protocol,SPICE/spice-protocol,fgouget/spice-protocol,vdiot/spice-protocol,SPICE/spice-protocol,SPICE/spice-protocol