bus: make sd_bus_request_name() and sd_bus_release_name() behave more like other...

bus: make sd_bus_request_name() and sd_bus_release_name() behave more like other calls

Instead of returning an enum of return codes, make them return error
codes like kdbus does internally.

Also, document this behaviour so that clients can stick to it.

(Also rework bus-control.c to always have to functions for dbus1 vs.
kernel implementation of the various calls.)