There is a race condition between dapl_rbuf_add() dapl_rbuf_remove() when

There is a race condition between dapl_rbuf_add() dapl_rbuf_remove() when
the ring buffer is empty or full. This could lead to incorrect item be
dequeued and correct item be discarded.

A temporary workaround is provided to ensure the pending event queue work
correctly. Without this fix dapl_evd_dequeue() could return the wrong event
and causes various application errors (hanging, assertion failures. etc).

Ultimately the ring buffer mechanism needs to the fixed.