ipv4: clarify the range of broken freebsd kernel versions
ipv4: clarify the range of broken freebsd kernel versions

Change-Id: Ic37732f28e747c98cb513e100983d685efd3928d
Reviewed-on: https://go-review.googlesource.com/c/net/+/173077
Run-TryBot: Mikio Hara <7d2a5fb8aa07e3795b8006c20159dd02aea6b94f@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/net