ReplicatedPG::cancel_copy: clear cop->obc

Otherwise, an objecter callback might still be hanging
onto this reference until after the flush.

Fixes: #8894
Introduced: 589b639af7c8834a1e6293d58d77a9c440107bc3
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG::maybe_handle_cache: do not forward RWORDERED reads

Even with READFORWARD, we can't forward RWORDERED reads.

Fixes: #9119
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #2268 from ceph/wip-9119

Wip 9119

Reviewed-by: Sage Weil <sage@redhat.com>