syscall: rename SysProcAttr.Unshare to Unshareflags

For symmetry with Cloneflags and it looks slightly weird because there
is syscall.Unshare method.

Change-Id: I3d710177ca8f27c05b344407f212cbbe3435094b
Reviewed-on: https://go-review.googlesource.com/23612
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go
index 0997563..395dd99 100644
--- a/src/syscall/exec_linux_test.go
+++ b/src/syscall/exec_linux_test.go
@@ -143,7 +143,7 @@
 
 	cmd := exec.Command("cat", "/proc/net/dev")
 	cmd.SysProcAttr = &syscall.SysProcAttr{
-		Unshare: syscall.CLONE_NEWNET,
+		Unshareflags: syscall.CLONE_NEWNET,
 	}
 	out, err := cmd.CombinedOutput()
 	if err != nil {