According to Tailscale SaaS behavior, autogroup:internet is handled
by exit node routing via AllowedIPs, not by packet filtering. ACL
rules with autogroup:internet as destination should produce no
filter rules for any node.
Previously, Headscale expanded autogroup:internet to public CIDR
ranges and distributed filters to exit nodes (because 0.0.0.0/0
"covers" internet destinations). This was incorrect.
Add detection for AutoGroupInternet in filter compilation to skip
filter generation for this autogroup. Update test expectations
accordingly.
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