Proposed change for bhyve DEBUG_HDA

Hi,

I noticed we are unconditionally enabling DEBUG_HDA in bhyve. This can 
cause /tmp to fill up unexpectedly.

I created a code review proposing to change the default:

https://reviews.freebsd.org/D39826

I also discovered that the code actually fails to build if DEBUG_HDA is 
disabled. Review contains fix for this too.

Not sure who should review it, but I thought to post a message here to 
make sure interested people know about this review.

Thanks in advance!

-- 
Guido Falsi <mad@madpilot.net>