Add update and delete subnet operations :cool:
diff --git a/openstack/networking/v2/subnets/errors.go b/openstack/networking/v2/subnets/errors.go
index 9299927..ca2df72 100644
--- a/openstack/networking/v2/subnets/errors.go
+++ b/openstack/networking/v2/subnets/errors.go
@@ -7,7 +7,9 @@
 }
 
 var (
-	ErrNetworkIDRequired = err("A network ID is required")
-	ErrCIDRRequired      = err("A valid CIDR is required")
-	ErrInvalidIPType     = err("An IP type must either be 4 or 6")
+	ErrNetworkIDRequired     = err("A network ID is required")
+	ErrCIDRRequired          = err("A valid CIDR is required")
+	ErrInvalidIPType         = err("An IP type must either be 4 or 6")
+	ErrCIDRNotUpdatable      = err("CIDR attributes cannot be updated")
+	ErrIPVersionNotUpdatable = err("IP Version attributes cannot be updated")
 )