ei: require the client to confirm capabilities rather than drop them
Our API requires a client to know which capability to pass into the drop_capabilities function. This doesn't work for capabilities newer than the client's version so they do not get disabled. The client will thus receive devices it didn't ask for and doesn't know how to handle.
Let's invert the requirement and require the caller to confirm the capabilities it wants - all others are dropped.
This is an API break but also requires updates of all clients, the previous simple case of just calling ei_seat_bind() will now result in zero capabilities.