Ignore ECONNRESET on close

FreeBSD returns ECONNRESET in certain (unclear) circumstances, but it
does still close the FD successfully. If you care about this case, you
should probably use `shutdown` instead and check for it there.

Python and Ruby at least both explicitly check for and ignore this error
too.

lib_eio_posix/flow.ml

@@ -119,7 +119,12 @@ module Impl = struct
 
   let fd t = t
 
-  let close = Eio_unix.Fd.close
+  let close t =
+    try
+      Eio_unix.Fd.close t
+    with Unix.Unix_error (ECONNRESET, _, _) ->
+      (* For FreeBSD. See https://github.com/ocaml-multicore/eio/issues/786 *)
+      ()
 end
 
 let handler = Eio_unix.Pi.flow_handler (module Impl)