cmd: update vendored golang.org/x/sys/unix

This pulls in CL 164497.

Fixes #24771

Change-Id: I88f2062e2c42363591dcb9e592a7a8381268ddeb
Reviewed-on: https://go-review.googlesource.com/c/164460Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/vendor/golang.org/x/sys/unix/sockcmsg_unix.go

@@ -25,8 +25,8 @@ func cmsgAlignOf(salen int) int {
 		if SizeofPtr == 8 {
 			salign = 4
 		}
-	case "openbsd":
-		// OpenBSD armv7 requires 64-bit alignment.
+	case "netbsd", "openbsd":
+		// NetBSD and OpenBSD armv7 require 64-bit alignment.
 		if runtime.GOARCH == "arm" {
 			salign = 8
 		}

src/cmd/vendor/vendor.json

@@ -135,10 +135,10 @@
 			"revisionTime": "2018-05-24T11:38:20Z"
 		},
 		{
-			"checksumSHA1": "v0kuTLSywKZmIwuyR3JyT18CgZk=",
+			"checksumSHA1": "/4HmlX92To16u5s2bryHkTS4+CM=",
 			"path": "golang.org/x/sys/unix",
-			"revision": "cc5685c2db1239775905f3911f0067c0fa74762f",
-			"revisionTime": "2019-02-24T20:24:49Z"
+			"revision": "a34e9553db1e492c9a76e60db2296ae7e5fbb772",
+			"revisionTime": "2019-02-28T12:11:59Z"
 		},
 		{
 			"checksumSHA1": "/G/UvW6DnpLWoplv0wkB3JunvXk=",