bus: sync with kdbus

Two new things here:

a) struct kdbus_notify_name_change now carries two struct
   kdbus_notify_id_change

b) a new KDBUS_CMD_BYEBYE ioctl that has no user yet in systemd
tests: fix build
bus: when releasing, taking, listing bus names check if they are valid

Given that the kernel does not validate bus names we have to when using
them.
bus: beef up driverd

Add validity checks for all parameters passed in.

Implement ReleaseName and StartServiceByName().

Fix access control in vtable.
busctl: output a single sorted list of names, including activatable and activated
core,logind,networkd: don't pick up devices from udev before they finished udev initialization

Managers shouldn't pick up the devices the manage before udev finished
initialization, hence check explicitly for that.
comment out udev's is_initialized call until the problem is sorted out
login: Don't stop a running user manager from garbage-collecting the user.

With the current logic, a user will never be garbage-collected, since its
manager will always be around. Change the logic such that a user is
garbage-collected when it has no sessions and linger is disabled.