internal/clientinfo: skipping non-reachable neighbor

Otherwise, failed or stale ipv6 will be used if it appeared last in the
table, instaed of the current one.

internal/clientinfo/ndp_linux.go

@@ -15,9 +15,12 @@ func (nd *ndpDiscover) scan() {
 	}
 
 	for _, n := range neighs {
+		// Skipping non-reachable neighbors.
+		if n.State&netlink.NUD_REACHABLE == 0 {
+			continue
+		}
 		ip := n.IP.String()
 		mac := n.HardwareAddr.String()
 		nd.saveInfo(ip, mac)
 	}
-
 }