eis: server must be able to disable unknown capabilities
Right now, the server can use eis_device_disable_capability
to disable a capability but that only works where the cap is known to the server. Without that call, the cap is implicitly allowed and that won't work for a new capability that the server doesn't yet know about.
Need to either switch to eis_device_allow_capability()
or have some other way of masking out unknown capabilities.