v3.0.x: fix stall in opal_fifo test

[jsquyres]

Filing a blocker to make sure we don't release the next v3.0.x without fixing #3450, possibly by PR #3468.

[hjelmn]

I think this is fixed now.

[jsquyres]

@hppritcha @bwbarrett Nathan thinks this is fixed, and I confirm that the issue / PR cited in this issue are both closed.

Do one of you v3.x RMs want to close this issue?