Restrict netlink

Fixed upstream since 0.3.1.

Author: emillon

packages/netlink/netlink.0.2.1/opam

@@ -16,7 +16,7 @@ remove: [
 depends: [
   "ocaml" {< "5.0.0"}
   "ocamlfind"
-  "ctypes"
+  "ctypes" {< "0.21.0"}
   "ctypes-foreign"
   "ocamlbuild" {build}
 ]