FBSD restore old syscall register logic for older kernels

FBSD  restore old syscall register logic for older kernels

The syscall_register code appears to depend on coordination
with FreeBSD upstream, which hopefully can be completed by
RELENG_9.  Use the original code for installation of the AFS
syscall everything older than that.

Change-Id: I2954cf1a2ae3587a311e8133ec5cdc500b4e2e24
Reviewed-on: http://gerrit.openafs.org/2618
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>