On 11.2-RELEASE or above FreeBSD kernels, the breakage of routing
message alignment for 386 emulation (see COMPAT_FREEBSD32 in
sys/net/rtsock.c) is fixed. This change makes packages in the x/net
repository work regardless of the kernel fix.

Change-Id: Ie71cc7dfb842c66225f96d1fb0e8cc5de7c47015
Reviewed-on: https://go-review.googlesource.com/c/139577Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>