bus-driverd: do not track identical matches

Identical matches are only one time in the hash map but multiple
times in the list; when removing, the hash will be empty but the
list still has entries.

Not adding dupicates to the list should keep us in sync and prevent
hitting the assert.
bus: use existing macros from def.h
bus: export bus address also when compiled without kdbus

It was removed from user@.service, so it should be added here.