[PATCH] NBD: cosmetic cleanups

From: Lou Langholtz <ldl@aros.net>

It's a helpful step in being better able to identify code inefficiencies
and problems particularly w.r.t.  locking.  It also modifies some of the
output messages for greater consistancy and better diagnostic support.

This second patch is a lead in that way to the third patch, which will
simply introduce the dprintk() debugging facility that my jumbo patch
originally had.

With the cosmetics patch and debugging enhancement (patch), it will make it
easier to fix or at least improve the locking bugs/races in NBD (that will
likely make up the fourth patch in my envisioned roadmap).