The variable name compatFreeBSD32 refers to the kernel configuration
directive COMPAT_FREEBSD32 and is also used in route and ipv6 packages.

Change-Id: I00e6de390c25b7df45b76e772719a83fa6b0843b
Reviewed-on: https://go-review.googlesource.com/c/149879Reviewed-by: Ian Lance Taylor <iant@golang.org>