treewide: use enum for `odb_for_each_object()` flags

treewide: use enum for `odb_for_each_object()` flags

We've got a couple of callsites where we pass `odb_for_each_object()`
flags, but accept an `unsigned` flags field instead of the corresponding
enum. Adapt these to accept the enum type instead.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>