ssh/tailssh: fix /usr/bin/login args on macOS

Fixes #4931

Signed-off-by: Adam Eijdenberg <adam@continusec.com>

ssh/tailssh/incubator_darwin.go

@@ -0,0 +1,9 @@
+// Copyright (c) 2022 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.
+
+package tailssh
+
+func (ia *incubatorArgs) loginArgs() []string {
+	return []string{ia.loginCmdPath, "-fp", "-h", ia.remoteIP, ia.localUser}
+}