internal/nettest: drop causesIPv6Crash

The causesIPv6Crash helper function was only needed on macOS 10.8 and
before. However, Go 1.11 requires at least macOS 10.11, so drop the
check altogether. Also remove the unused implementations for all other
geese.

Change-Id: I7459f942374e7e2e6c14b787e2dfc493de67bedc
Reviewed-on: https://go-review.googlesource.com/c/156497
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

internal/nettest/helper_bsd.go

@@ -8,28 +8,8 @@ package nettest
 
 import (
 	"runtime"
-	"strconv"
-	"strings"
-	"syscall"
 )
 
-var darwinVersion int
-
-func init() {
-	if runtime.GOOS == "darwin" {
-		// See http://support.apple.com/kb/HT1633.
-		s, err := syscall.Sysctl("kern.osrelease")
-		if err != nil {
-			return
-		}
-		ss := strings.Split(s, ".")
-		if len(ss) == 0 {
-			return
-		}
-		darwinVersion, _ = strconv.Atoi(ss[0])
-	}
-}
-
 func supportsIPv6MulticastDeliveryOnLoopback() bool {
 	switch runtime.GOOS {
 	case "freebsd":
@@ -38,16 +18,7 @@ func supportsIPv6MulticastDeliveryOnLoopback() bool {
 		// kernels don't deliver link-local scoped multicast
 		// packets correctly.
 		return false
-	case "darwin":
-		return !causesIPv6Crash()
 	default:
 		return true
 	}
 }
-
-func causesIPv6Crash() bool {
-	// We see some kernel crash when running IPv6 with IP-level
-	// options on Darwin kernel version 12 or below.
-	// See golang.org/issues/17015.
-	return darwinVersion < 13
-}

internal/nettest/helper_nobsd.go

@@ -9,7 +9,3 @@ package nettest
 func supportsIPv6MulticastDeliveryOnLoopback() bool {
 	return true
 }
-
-func causesIPv6Crash() bool {
-	return false
-}

internal/nettest/helper_stub.go

@@ -23,10 +23,6 @@ func supportsIPv6MulticastDeliveryOnLoopback() bool {
 	return false
 }
 
-func causesIPv6Crash() bool {
-	return false
-}
-
 func protocolNotSupported(err error) bool {
 	return false
 }

internal/nettest/helper_windows.go

@@ -36,7 +36,3 @@ func supportsRawIPSocket() (string, bool) {
 func supportsIPv6MulticastDeliveryOnLoopback() bool {
 	return true
 }
-
-func causesIPv6Crash() bool {
-	return false
-}