allow bulk op insert for w:0 bulk inserts

o fixes a performance regression for 2.6 w:0 writes
o allows w:0 writes to fast path out of the bulk api on 2.4

Author: hanumantmk

src/mongoc/mongoc-bulk-operation.c

@@ -177,7 +177,8 @@ mongoc_bulk_operation_insert (mongoc_bulk_operation_t *bulk,
    }
 
    _mongoc_write_command_init_insert (&command, &document, 1, bulk->ordered,
-                                      false);
+      !_mongoc_write_concern_has_gle (bulk->write_concern));
+
    _mongoc_array_append_val (&bulk->commands, command);
 
    EXIT;