interfaces: create android impl (#11784)

-Move Android impl into interfaces_android.go
-Instead of using ip route to get the interface name, use the one passed in by Android (ip route is restricted in Android 13+ per termux/termux-app#2993)

Follow-up will be to do the same for router

Fixes tailscale/corp#19215
Fixes tailscale/corp#19124

Signed-off-by: kari-ts <kari@tailscale.com>

net/interfaces/interfaces_defaultrouteif_todo.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !linux && !windows && !darwin && !freebsd
+//go:build !linux && !windows && !darwin && !freebsd && !android
 
 package interfaces