os/bluestore: keep ref to deleted onode in _do_remove

We need to make sure we carry this ref through until the object is
deleted or else another request right try to read it before the kv
txn is applied.  (This is easy to trigger now that onreadable is completed
at queue time instead of commit time.)

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 0347518)

src/os/bluestore/BlueStore.cc

@@ -10966,6 +10966,7 @@ int BlueStore::_do_remove(
   txc->removed(o);
   o->extent_map.clear();
   o->onode = bluestore_onode_t();
+  txc->note_modified_object(o);
   _debug_obj_on_delete(o->oid);
 
   if (!is_gen || maybe_unshared_blobs.empty()) {