systemd-networkd-wait-online logic

If one or more --interface options are given, then exactly those interfaces are considered.
(--ignore options and RequiredForOnline=false have no effect in this case)

If no --interface option is given, all detected interfaces are considered except:
- the loopback interface
- interfaces excluded using --ignore
- interfaces with RequiredForOnline=false


Condition for systemd-networkd-wait-online to succeed:

with --any option:
	at least one of the interfaces must be "ready" (defined below).

without --any option, with one or more --interface options:
	all of the interfaces must be "ready".

without --any option, without --interface options:
	at least one of the interfaces must be "ready".
	none of the interfaces may be "unconfigured".


where "unconfigured" means the link state is any of:
- unknown (still being processed by udev)
- pending
- configuring

and "ready" means the interface
1. is not "unconfigured", and
2. has operstate within the range given by (from highest to lowest priority):
	- from --interface=INTERFACE:MIN_OPERSTATE[:MAX_OPERSTATE]
	- from --operational-state=MIN_OPERSTATE[:MAX_OPERSTATE]
	- from RequiredForOnline=MIN_OPERSTATE[:MAX_OPERSTATE
	- default: >= degraded
(An interface specified via --interface is also considered to be "ready" if the
interface doesn't exist and the MIN_OPERSTATE is "missing".)