doctor/ethtool, ipn/ipnlocal: add ethtool bugreport check

Updates #11137

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Idbe862d80e428adb044249c47d9096b87f29d5d8

doctor/ethtool/ethtool_other.go

@@ -0,0 +1,17 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !linux
+
+package ethtool
+
+import (
+	"runtime"
+
+	"tailscale.com/types/logger"
+)
+
+func ethtoolImpl(logf logger.Logf) error {
+	logf("unsupported on %s/%s", runtime.GOOS, runtime.GOARCH)
+	return nil
+}