ipn/ipnlocal: fix app connector route advertisements on exit nodes

If an app connector is also configured as an exit node, it should still
advertise discovered routes that are not covered by advertised routes,
excluding the exit node routes.

Updates tailscale/corp#16928

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f