Add find peer success addr to peerstore (#296)

When a peer is found, add its addr to the peerstore, just like the addresses for closer peers are added. In particular this is helpful for followup queries by the DHT user.

query.go

@@ -297,6 +297,9 @@ func (r *dhtQueryRunner) queryPeer(proc process.Process, p peer.ID) {
 		r.Lock()
 		r.result = res
 		r.Unlock()
+		if res.peer != nil {
+			r.query.dht.peerstore.AddAddrs(res.peer.ID, res.peer.Addrs, pstore.TempAddrTTL)
+		}
 		go r.proc.Close() // signal to everyone that we're done.
 		// must be async, as we're one of the children, and Close blocks.