The masks are checked in win32u, and updated if necessary, right before waiting for messages. They tell wineserver which of the bits we want the queue to be signaled for in the following wait.
There should be no need to clear the mask after waiting, and doing it will always force clients to update them again on the next wait, causing an additional request.
-- v2: server: Remove skip_wait flag from set_queue_mask. server: Do not clear queue masks in msg_queue_satified. server: Rename queue is_signaled to get_queue_status.