on the card, unmap it first. This allows it to be picked up properly when
the queue gets kicked again. This was the root problem for the lost command
(i.e. stuck in getblk/vinvalb) problem. While here, panic if commands don't
map correctly instead of just silently ignoring the problem and dropping
command. Also slow down the dynamic allocation of new commands.
It should be safe to go back into the aac waters. Thanks to everyone who
suffered through this and provided good feedback.
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