asg: Tweak how window is calculated

bug: 140112486

Just use a count of outstanding instead of
the complicated atomics.

Also, don't use the entire window range or bad stuff happens.

(TODO: shoudl be able to do window range - 1 slots)

Change-Id: I5499e3c26bcfb5bbf04d0a2c642fb80fb8035b16
2 files changed