Depends on dbus service rather than socket

With newer dbus depending on dbus.socket doesn't work and block the boot.
Instead of this we should do probably Wants=dbus.service, then sensorfw could start before dbus.service is started and start initializing things. Yes, it blocks until dbus.service is up but that is the purpose as well, to allow different services to start side by side before others are ready to allow faster bootup.