loopback-setup: correctly set flags and scope for ipv6 address
rtnl: correctly get the size of data to be appended

This fixes:
  systemd[1]: Failed to configure loopback device: Numerical result out of range
remove unused variable
bus: reenable id change subscriptions
bus: fix exit-on-idle for driverd
machined: implement exit-on-idle
service: don't send out PropertiesChanged message for each watchdog notification
sd-event: return 1 in sd_event_run() when we hit EINTR

That way we can distuingish timeouts from EINTR
def: lower exit-on-idle time