freebsd: track RELENG_8

freebsd: track RELENG_8

Fixes to re-enable build and load of kernel module on FreeBSD's
RELENG_8.  Includes the following changes:

Remove cred pointer argument to vop_getattr and vop_setattr.
Restore VSUID and VGUID defines, but move to osi_machdep.h.
Fixup calls to vinvalbuf, create a macro to avoid too many ifdefs.
Revert incorrect definition of gop_lookupname_user.  Avoid
uninitialized use of 'code' variable in vop_access, and track
new a_accmode member name.  Remove cred pointer in VFS_STATFS.
Avoid including sys/ioctl.h in kernel mode (formerly had no
effect, it's now an error).  Avoid using an empty file as an
object file in shlibafsrpc link.  Replace suser() calls with calls
to priv_check, using defined OpenAFS privileges (thanks due to
Ben Kaduk).

Change-Id: I96fc29599a797b975630c8fa5b8b84798b3740a6
Reviewed-on: http://gerrit.openafs.org/1023
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>