Catch up to FreeBSD KPI for vfs_cmount

Almost a year ago, mckusick changed the VFS KPI/KBI for the cmount
VFS operation, making the flags argument a 64-bit quantity.
Introduce appropriate conditionals for our prototype of afs_cmount
for the change on the 10.x and 9.x branches.

Reviewed-on: http://gerrit.openafs.org/8907
Reviewed-by: Garrett Wollman <wollman@csail.mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 13111d25408cf6765d1b67bc3767614c8963cfde)

Change-Id: I6e74760422f57336203d562dc4ee39ed2af0df84
Reviewed-on: http://gerrit.openafs.org/9406
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>