agent: Add macro for clearing capability
agent: Add macro for clearing capability

Related:
https://bugzilla.redhat.com/show_bug.cgi?id=1373725

Acked-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

fgouget/spice-protocol,fgouget/spice-protocol,fgouget/spice-protocol