clients: keep generic device records

Now that we display connected clients in the status page,
it makes sense that we show all of them, instead of only
recognized device types.
cosmetic: whitespace cleanup
ssdp: send a full byebye + alive set when a new interface comes online

If an interface comes online after startup, we really need to send a
complete byebye + alive set on that interface, but we don't want to do
it for other interfaces.  So do it as the interfaces come up, and
skip it for interfaces that existed before the reload.
ssdp: add multicast membership as the individual interfaces come up

Previously, this was only done during startup, so interfaces that
came up later wouldn't have been added.