net: drop confusing comment

On AIX, we don't need to be aware of any change on the protocol stack of
Linux kernel.

Change-Id: Ib8b14fa930acddb3bc720d401271e8daf567b784
Reviewed-on: https://go-review.googlesource.com/c/157298
Run-TryBot: Mikio Hara <mikioh.public.networking@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/sockopt_aix.go

@@ -9,8 +9,6 @@ import (
 	"syscall"
 )
 
-// This was copied from sockopt_linux.go
-
 func setDefaultSockopts(s, family, sotype int, ipv6only bool) error {
 	if family == syscall.AF_INET6 && sotype != syscall.SOCK_RAW {
 		// Allow both IP versions even if the OS default