Add gophercloud openstack/networking/v2/extensions

Aka github.com/rackspace/gophercloud/openstack/networking/v2/extensions

vendor/github.com/rackspace/gophercloud/openstack/common/extensions/urls.go

@@ -0,0 +1,13 @@
+package extensions
+
+import "github.com/rackspace/gophercloud"
+
+// ExtensionURL generates the URL for an extension resource by name.
+func ExtensionURL(c *gophercloud.ServiceClient, name string) string {
+	return c.ServiceURL("extensions", name)
+}
+
+// ListExtensionURL generates the URL for the extensions resource collection.
+func ListExtensionURL(c *gophercloud.ServiceClient) string {
+	return c.ServiceURL("extensions")
+}