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
libsystemd-bus: follow changes in kdbus

In particular, the match interface has seen a major overhaul.
libsystemd-bus: match on any connection ID unless specified
bus: wrap KDBUS_CMD_BYEBYE with a high-level call sd_bus_try_close()
update TODO
core: pass notify fd across reexecs

That way we the random socket name stays stable across reexec and we
won't lose client messages.
bus: when watching bus names, we always need to add a change match

Since for the kernel change of ownership of a name between starter and
real client is a change and for userspace thats addition/removal, we
need to unconditionally subscribe to these change events.
core: make check for Disconnected message more precise
bus: when filtering by sender take well known names lest from attached creds into account
bus: always consider well-known names sender credentials as attached to messages
bus: always override message destination field with data from kdbus
bus: in sd_bus_try_close() consider local read queue too