isert: convert to the new CQ API and a few random cleanups V2

Christoph Hellwig
2016-02-22T13:49:13Z

This series uses the new CQ API and cleans up a few random lose arounds
around the R/W path. I have a few more changes for the RW path in the
works, but I think this is a good enough standalone series for now.

Changes since V1:

- sort out pre-existing confusion about the login buffer sizes
- add various little inline helpers for container_of constructs
- assign the ->done handlers only once
- updates commit messages