dix: ensure work queues are cleared on reset
If the server resets, most client workqueues are cleaned up as the clients are killed.
The one exception is the server's client, which is exempt from the killing spree.
If that client has a queued work procedure active, it won't get cleared on reset.
This commit ensures it gets cleared too.
(cherry picked from commit 8738ce85)
Fixes: #670 (closed)