migrate to upstream libcompose in one and a half go

vendor/github.com/docker/libnetwork/default_gateway_linux.go

@@ -0,0 +1,29 @@
+package libnetwork
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/docker/libnetwork/drivers/bridge"
+	"github.com/docker/libnetwork/netlabel"
+	"github.com/docker/libnetwork/options"
+)
+
+func (c *controller) createGWNetwork() (Network, error) {
+	netOption := map[string]string{
+		bridge.BridgeName:         libnGWNetwork,
+		bridge.EnableICC:          strconv.FormatBool(false),
+		bridge.EnableIPMasquerade: strconv.FormatBool(true),
+	}
+
+	n, err := c.NewNetwork("bridge", libnGWNetwork,
+		NetworkOptionGeneric(options.Generic{
+			netlabel.GenericData: netOption,
+			netlabel.EnableIPv6:  false,
+		}))
+
+	if err != nil {
+		return nil, fmt.Errorf("error creating external connectivity network: %v", err)
+	}
+	return n, err
+}