Peer advertisement should get use PeerTracker for fromPeer

Since PeerTracker tracks connected peers and routes are propagated asynchronously, we can easily end up in a situation where we are propagating routes from a disconnected peer.

This is especially true with Graceful Restart and LLGR, where the routes are retained for a potentially long time.

Rather than relying on PeerTracker, LocRibWriter should be observing DTCNs from peer structure to have this information available, as that will mean it will:

• be immutable as appropriate
• it will propagate with routes, sharing the vector