networkd: properly track addresses when first added

networkd: properly track addresses when first added

When doing a NEWADDR, the reply we get back is the NEWADDR itself, rather
than just an empty ack (unlike how NEWLINK works). For this reason, the
process that did the NEWADDR does not get the broadcast message.

We were only listening for broadcast messages, and hence not tracking the
addresses we added ourselves. This went unnoticed as the kernel will usually
send NEWADDR messages from time to time anyway, so things would mostly work,
but in the worst case we would not notice that a routable address was available
and consider ourselves offline.