network: Reduce cyclomatic complexity

Added a new `deleteRoutes()` called from `updateRoutes()` to reduce the
complexity of the latter and keep the linters happy.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

network.go

@@ -278,6 +278,34 @@ func getInterface(netHandle *netlink.Handle, link netlink.Link) (*pb.Interface,
 // Routes //
 ////////////
 
+func (s *sandbox) deleteRoutes(netHandle *netlink.Handle) error {
+	if netHandle == nil {
+		return errNoHandle
+	}
+
+	initRouteList, err := netHandle.RouteList(nil, netlink.FAMILY_ALL)
+	if err != nil {
+		return err
+	}
+	for _, initRoute := range initRouteList {
+		// don't delete routes associated with lo:
+		link, _ := netHandle.LinkByIndex(initRoute.LinkIndex)
+		if link.Attrs().Name == "lo" || link.Attrs().Name == "::1" {
+			continue
+		}
+
+		err = netHandle.RouteDel(&initRoute)
+		if err != nil {
+			//If there was an error deleting some of the initial routes,
+			//return the error and the current routes on the system via
+			//the defer function
+			return err
+		}
+	}
+
+	return nil
+}
+
 //updateRoutes will take requestedRoutes and create netlink routes, with a goal of creating a final
 // state which matches the requested routes.  In doing this, preesxisting non-loopback routes will be
 // removed from the network.  If an error occurs, this function returns the list of routes in
@@ -304,26 +332,9 @@ func (s *sandbox) updateRoutes(netHandle *netlink.Handle, requestedRoutes *pb.Ro
 	// is designed to be declarative, so we will attempt to create state matching what is
 	// requested, and in the event that we fail to do so, will return the error and final state.
 	//
-
-	initRouteList, err := netHandle.RouteList(nil, netlink.FAMILY_ALL)
-	if err != nil {
+	if err = s.deleteRoutes(netHandle); err != nil {
 		return nil, err
 	}
-	for _, initRoute := range initRouteList {
-		// don't delete routes associated with lo:
-		link, _ := netHandle.LinkByIndex(initRoute.LinkIndex)
-		if link.Attrs().Name == "lo" || link.Attrs().Name == "::1" {
-			continue
-		}
-
-		err = netHandle.RouteDel(&initRoute)
-		if err != nil {
-			//If there was an error deleting some of the initial routes,
-			//return the error and the current routes on the system via
-			//the defer function
-			return
-		}
-	}
 
 	//
 	// Set each of the requested routes