osd: always send returnvec-on-errors for client's retry

osd: always send returnvec-on-errors for client's retry

Currently there is a discrepancy in terms of the returnvec's
presence between MOSDOpReplys sent for original requests and
those on dups. The former always contain the returnvec if
an error happened, even if `allows_returnvec()` is `false`.

This commit extends the behavior on dups.

For RCA please see: https://tracker.ceph.com/issues/64192#note-9

Fixes: https://tracker.ceph.com/issues/64192
Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>