tailscale-android doesn't update android VPN configuration when advertised subnets change

Version: Tailscale 1.24.2-tdce2409b1-gb8ed6272bdb on Pixel6 with Android 12

Steps:
* Set a node as a subnet router, approve in the admin panel, etc
* Note that android is able to route to the subnet
* Add a new subnet to the subnet router, approve in the admin panel, etc

Expected:
* Android can immediately reach the new subnets

Actual:
* Android doesn't see the new subnets right away
* If you logout -> login on android, it picks up the new routes.

This sounds like we aren't correctly updating the android OS's routing table on incremental changes. I'm told we previously had a similar problem when turning Exit Nodes on and off, which we worked around using a hack in the UI. It sounds like the timing for when to re-register routes should be in the backend instead, to avoid increasingly rare edge cases like this.

Reported by twitter user imksoo: https://twitter.com/imksoo/status/1536837841627451392