completion timeouts with pin-based interrupts in QEMU hw/nvme

[Keith Busch]

Klaus,

This isn't going to help your issue, but there are at least two legacy
irq bugs in the nvme qemu implementation.

1. The admin queue breaks if start with legacy and later initialize
msix.

2. The legacy vector is shared among all queues, but it's being
deasserted when the first queue's doorbell makes it empty. It should
remain enabled if any cq is non-empty.

I'll send you some patches for those later. Still working on the real
problem.