osc/pt2pt: Grab the accumulate lock, not the module lock, when appending.

 * Otherwise one thread could be in `opal_list_append` while the second
   is in `opal_list_remove_first` in `ompi_osc_pt2pt_progress_pending_acc`
   - The former was holding the `module` lock, while the latter was holding
     the `accumulate` lock so neither was properly protected.
   - This resulted in a segv when there was concurrent access.

Author: jjhursey

ompi/mca/osc/pt2pt/osc_pt2pt_data_move.c

@@ -747,7 +747,9 @@ static int ompi_osc_pt2pt_acc_op_queue (ompi_osc_pt2pt_module_t *module, ompi_os
     }
 
     /* add to the pending acc queue */
-    OPAL_THREAD_SCOPED_LOCK(&module->lock, opal_list_append (&module->pending_acc, &pending_acc->super));
+    ompi_osc_pt2pt_accumulate_lock(module);
+    opal_list_append (&module->pending_acc, &pending_acc->super);
+    ompi_osc_pt2pt_accumulate_unlock(module);
 
     return OMPI_SUCCESS;
 }