The variable name compatFreeBSD32 refers to the kernel configuration
directive COMPAT_FREEBSD32 and is also used in route and ipv4 packages.

Change-Id: Ia6f123833af0c11398f46dfa31c3e5c5ab121fc0
Reviewed-on: https://go-review.googlesource.com/c/149878Reviewed-by: Ian Lance Taylor <iant@golang.org>