feature/logtail: pull logtail + netlog out to modular features

Removes 434 KB from the minimal Linux binary, or ~3%.

Primarily this comes from not linking in the zstd encoding code.

Fixes #17323

Change-Id: I0a90de307dfa1ad7422db7aa8b1b46c782bfaaf7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/netlog/netlog.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_netlog && !ts_omit_logtail
+
 // Package netlog provides a logger that monitors a TUN device and
 // periodically records any traffic into a log stream.
 package netlog

wgengine/netlog/netlog_omit.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_netlog || ts_omit_logtail
+
+package netlog
+
+type Logger struct{}
+
+func (*Logger) Startup(...any) error { return nil }
+func (*Logger) Running() bool        { return false }
+func (*Logger) Shutdown(any) error   { return nil }
+func (*Logger) ReconfigRoutes(any)   {}