nvme: Move AER processing into a task thread

[imp]

Summary

Move the AER processing into the taskqueue thread. We do memory
allocations and such burried deep in things we call, so this just makes
all that simpler and doesn't stall the completion thread. It fixes a few
panics if you get a reliability failure from the drive at the wrong
time.

Sponsored by: Netflix

[imp]

We see about 1-3 crashes a month from this from our fleet of NVMe drives at work...

[imp]

sys/dev/nvme/nvme_ctrlr.c

1176

For the record, I think we shouldn't be doing this byte swapping and should use the appropriate leXXtohost() functions where we use the data, but that's a bigger change for another day. Also, I don't have BE hardware to test this on.

[jhb]

nvmf already uses a taskqueue for this for the same reasons.

[imp]

In D51416#1175601, @jhb wrote:

nvmf already uses a taskqueue for this for the same reasons.

Yea, I need to close this since I'd accidentally pushed this when I was pushing other changes.

[imp]

This landed in b21e67875bf0c4b1e7933090b80307abb24b7d03 (by mistake, so no autoclose)