We usually enqueue a number of these calls on each service
initialization. Let's do this asynchronously, and thus remove
synchronization points. This improves both performance behaviour and
reduces the chances to deadlock.
THe match cookie was used by kdbus to identify matches we install
uniquely. But given that kdbus is gone, the cookie serves no process
anymore, let's kill it.
Some kdbus_flag and memfd related parts are left behind, because they
are entangled with the "legacy" dbus support.
test-bus-benchmark is switched to "manual". It was already broken before
(in the non-kdbus mode) but apparently nobody noticed. Hopefully it can
be fixed later.
This makes callback behaviour more like sd-event or sd-resolve, and
creates proper object for unregistering callbacks.
Taking the refernce to the slot is optional. If not taken life time of
the slot will be bound to the underlying bus object (or in the case of
an async call until the reply has been recieved).
