wasm: exclude code that's not used on iOS for Wasm too

It has similar size constraints. Saves ~1.9MB from the Wasm build.

Updates #3157

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

wgengine/magicsock/debugknobs.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !ios
-// +build !ios
+//go:build !ios && !js
+// +build !ios,!js
 
 package magicsock
 

wgengine/magicsock/debugknobs_stubs.go

@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build ios || js
+// +build ios js
+
 package magicsock
 
 import "tailscale.com/types/opt"
 
-// All knobs are disabled on iOS.
+// All knobs are disabled on iOS and Wasm.
 // Further, they're const, so the toolchain can produce smaller binaries.
 const (
 	debugDisco                       = false