fixup! CP-32622: introduce select-as-epoll in Unixext

Author: edwintorok

ocaml/libs/xapi-stdext/lib/xapi-stdext-unix/unixext.ml

@@ -684,6 +684,8 @@ let pollerr_set = Polly.Events.pri
 
 let to_milliseconds ms = ms *. 1e3 |> ceil |> int_of_float
 
+(* we could change lists to proper Sets once the Unix.select to Unixext.select conversion is done *)
+
 let readable fd (rd, wr, ex) = (fd :: rd, wr, ex)
 
 let writable fd (rd, wr, ex) = (rd, fd :: wr, ex)