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_stubs.go

@@ -0,0 +1,24 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// 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 and Wasm.
+// Further, they're const, so the toolchain can produce smaller binaries.
+const (
+	debugDisco                       = false
+	debugOmitLocalAddresses          = false
+	debugUseDerpRouteEnv             = ""
+	debugUseDerpRoute       opt.Bool = ""
+	logDerpVerbose                   = false
+	debugReSTUNStopOnIdle            = false
+	debugAlwaysDERP                  = false
+)
+
+func inTest() bool { return false }