Fix up passthrough comments
Fix up passthrough comments

Fix up comments from commit f5af231109fe89679c752eca9f5269ea39a4352e
"tcmur: add tcmur_cmd_passthrough_handler support".

We need that code path to support type1 tcmu-runner handlers
that are queue_depth=1 or do their own threading/aio.

open-iscsi/tcmu-runner,open-iscsi/tcmu-runner,liuy/tcmu-runner,lxbsz/tcmu-runner,agrover/tcmu-runner