syscall: revert to pre-FreeBSD 10 / POSIX-2008 timespec field names in Stat_t on FreeBSD
CL 138595 introduced the new names when the hardcoded stat8 definitions was replaced
with a cgo generated one.
Fixes #29393
Updates #22448
Change-Id: I6309958306329ff301c17344b2e0ead0cc874224
Reviewed-on: https://go-review.googlesource.com/c/155958
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>