Correct the acknowledgment and the reset of a BAU
software-acknowledged message.
A retry message should be testing only for timed-out resources
(mask << 8). (And we delete a log message that might cause
unnecessary concern) The acknowledge MMR is
|--timed-out--|---pending--|, each is 8 bits.
The IPI-driven reset of software acknowledge resources frees
both timed out and pending resources.