vendor: update x/net/internal/nettest for aix support

Update golang.org/x/net/internal/nettest to x/net git rev 9b4f9f5ad519
for:

   internal/nettest: add AIX operating system
   https://golang.org/cl/144077

This fixes the build failure of the vendored x/net/internal/nettest on
aix/ppc64.

Additionally this also pulls in:

  all: re-adjust build constraints for JS and NaCl
  https://golang.org/cl/122539

Updates #25893

Change-Id: I9abefc7d4ad158e9e68913362f7f1320321d6f5f
Reviewed-on: https://go-review.googlesource.com/c/151301
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/vendor/golang_org/x/net/internal/nettest/helper_nobsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux solaris
+// +build aix linux solaris
 
 package nettest
 

src/vendor/golang_org/x/net/internal/nettest/helper_posix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris windows
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris windows
 
 package nettest
 

src/vendor/golang_org/x/net/internal/nettest/helper_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build js,wasm nacl plan9
+// +build js nacl plan9
 
 package nettest
 

src/vendor/golang_org/x/net/internal/nettest/helper_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
 package nettest
 

src/vendor/golang_org/x/net/internal/nettest/stack.go

@@ -72,7 +72,7 @@ func TestableNetwork(network string) bool {
 		}
 	case "unixpacket":
 		switch runtime.GOOS {
-		case "android", "darwin", "freebsd", "js", "nacl", "plan9", "windows":
+		case "aix", "android", "darwin", "freebsd", "js", "nacl", "plan9", "windows":
 			return false
 		case "netbsd":
 			// It passes on amd64 at least. 386 fails (Issue 22927). arm is unknown.