OpenBSD: Replace "vnodeop_desc" with "vops" in kernel module.

In OpenBSD 4.9, the vnode operations vector in the "vnode" struct
was changed from using a "vnodeop_desc" struct to a new "vops"
struct. This patch makes the appropriate changes to the OpenBSD
kernel module support to accommodate the change.

Reviewed-on: http://gerrit.openafs.org/8928
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit bb42c02ce56aec29e3860bec47e47157d0406f20)

Change-Id: I768358758763a362c92351211bda6d8a7eab6a26
Reviewed-on: http://gerrit.openafs.org/9595
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>