Build fix for recent FreeBSD -current

Build fix for recent FreeBSD -current

r273707 added a flags argument to syscall_register(), so
add the appropriate version check in param.generic_fbsd.h
and ues that in the main code.

Reviewed-on: http://gerrit.openafs.org/11565
Tested-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit f39dd54e11dff5e2b4da3eec419ae7c0825c210f)

Note that the 1.6 branch does not have param.generic_fbsd.h, so
the patch was modified for backport to just use AFS_FBSD110_ENV
as the conditional.

Change-Id: Id2934d83940caff4f64c2a7f2187b0eca5881c8f
Reviewed-on: http://gerrit.openafs.org/11610
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>