fix(linux_networking.go): filter routes to be deleted by table

Previously we were accidentally deleting all routes that were found,
this mimics the previous functionality better by only deleting external
IPs that were found in the externalIPRouteTable that are no longer in
the activeExternalIPs map.

Also improves logging around any routes that are deleted as this is
likely of interest to all kube-router administrators.

Author: aauren

pkg/controllers/proxy/linux_networking.go

@@ -631,13 +631,18 @@ func (ln *linuxNetworking) setupRoutesForExternalIPForDSR(serviceInfoMap service
 		}
 
 		// check if there are any pbr in externalIPRouteTableID for external IP's
-		routes, err := netlink.RouteList(nil, nFamily)
+		nRoute := &netlink.Route{
+			Family: nFamily,
+			Table:  externalIPRouteTableID,
+		}
+		routes, err := netlink.RouteListFiltered(nFamily, nRoute, netlink.RT_FILTER_TABLE)
 		if err != nil {
 			return fmt.Errorf("failed to list route for external IP's due to: %s", err)
 		}
 		for idx, route := range routes {
 			ip := route.Src.String()
 			if !activeExternalIPs[ip] {
+				klog.Infof("Deleting route: %+v in custom route table for external IP's as it is not active", route)
 				err = netlink.RouteDel(&routes[idx])
 				if err != nil {
 					klog.Errorf("Failed to del route for %v in custom route table for external IP's due to: %s",