Add three tests that verify control plane behavior for grant policies:
- TestGrantViaSubnetFilterRules: verifies the router's PacketFilter
contains destination rules for via-steered subnets. Without per-node
filter compilation for via grants, these rules were missing and the
router would drop forwarded traffic.
- TestGrantViaExitNodeFilterRules: same verification for exit nodes
with via grants steering autogroup:internet traffic.
- TestGrantIPv6OnlyPrefixACL: verifies that address-based aliases
(Prefix, Host) resolve to exactly the literal prefix and do not
expand to include the matching node's other IP addresses. An
IPv6-only host definition produces only IPv6 filter rules.
Updates #2180
Extend the servertest harness with:
- TestClient.Direct() accessor for advanced operations
- TestClient.WaitForPeerCount and WaitForCondition helpers
- TestHarness.ChangePolicy for ACL policy testing
- AssertDERPMapPresent and AssertSelfHasAddresses
New test suites:
- content_test.go: self node, DERP map, peer properties, user profiles,
update history monotonicity, and endpoint update propagation
- policy_test.go: default allow-all, explicit policy, policy triggers
updates on all nodes, multiple policy changes, multi-user mesh
- ephemeral_test.go: ephemeral connect, cleanup after disconnect,
mixed ephemeral/regular, reconnect prevents cleanup
- routes_test.go: addresses in AllowedIPs, route advertise and approve,
advertised routes via hostinfo, CGNAT range validation
Also fix node_departs test to use WaitForCondition instead of
assert.Eventually, and convert concurrent_join_and_leave to
interleaved_join_and_leave with grace-period-tolerant assertions.
