Support to config Flannel backend

- Add `flannel_backend_port` and `canal_flannel_backend_port` to config
the port of Flannel
- Add `flanneld_backend_vni` and `canal_flannel_backend_vni` to config
the VxLan network identify of Flannel

cluster/defaults.go

@@ -11,7 +11,7 @@ import (
 	"github.com/rancher/rke/log"
 	"github.com/rancher/rke/services"
 	"github.com/rancher/rke/templates"
-	v3 "github.com/rancher/types/apis/management.cattle.io/v3"
+	"github.com/rancher/types/apis/management.cattle.io/v3"
 )
 
 const (
@@ -50,6 +50,10 @@ const (
 	DefaultEtcdHeartbeatIntervalValue = "500"
 	DefaultEtcdElectionTimeoutName    = "election-timeout"
 	DefaultEtcdElectionTimeoutValue   = "5000"
+
+	DefaultFlannelBackendVxLan     = "vxlan"
+	DefaultFlannelBackendVxLanPort = "8472"
+	DefaultFlannelBackendVxLanVNI  = "1"
 )
 
 type ExternalFlags struct {
@@ -285,11 +289,15 @@ func (c *Cluster) setClusterNetworkDefaults() {
 		}
 	case FlannelNetworkPlugin:
 		networkPluginConfigDefaultsMap = map[string]string{
-			FlannelBackendType: "vxlan",
+			FlannelBackendType:                 DefaultFlannelBackendVxLan,
+			FlannelBackendPort:                 DefaultFlannelBackendVxLanPort,
+			FlannelBackendVxLanNetworkIdentify: DefaultFlannelBackendVxLanVNI,
 		}
 	case CanalNetworkPlugin:
 		networkPluginConfigDefaultsMap = map[string]string{
-			CanalFlannelBackendType: "vxlan",
+			CanalFlannelBackendType:                 DefaultFlannelBackendVxLan,
+			CanalFlannelBackendPort:                 DefaultFlannelBackendVxLanPort,
+			CanalFlannelBackendVxLanNetworkIdentify: DefaultFlannelBackendVxLanVNI,
 		}
 	}
 	if c.Network.CalicoNetworkProvider != nil {