wgengine/magicsock: enable setting relay epAddr's as bestAddr (#16229)

relayManager can now hand endpoint a relay epAddr for it to consider
as bestAddr.

endpoint and Conn disco ping/pong handling are now VNI-aware.

Updates tailscale/corp#27502
Updates tailscale/corp#29422

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/magicsock/peermap_test.go

@@ -0,0 +1,36 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package magicsock
+
+import (
+	"net/netip"
+	"testing"
+
+	"tailscale.com/types/key"
+)
+
+func Test_peerMap_oneRelayEpAddrPerNK(t *testing.T) {
+	pm := newPeerMap()
+	nk := key.NewNode().Public()
+	ep := &endpoint{
+		nodeID:    1,
+		publicKey: nk,
+	}
+	ed := &endpointDisco{key: key.NewDisco().Public()}
+	ep.disco.Store(ed)
+	pm.upsertEndpoint(ep, key.DiscoPublic{})
+	vni := virtualNetworkID{}
+	vni.set(1)
+	relayEpAddrA := epAddr{ap: netip.MustParseAddrPort("127.0.0.1:1"), vni: vni}
+	relayEpAddrB := epAddr{ap: netip.MustParseAddrPort("127.0.0.1:2"), vni: vni}
+	pm.setNodeKeyForEpAddr(relayEpAddrA, nk)
+	pm.setNodeKeyForEpAddr(relayEpAddrB, nk)
+	if len(pm.byEpAddr) != 1 {
+		t.Fatalf("expected 1 epAddr in byEpAddr, got: %d", len(pm.byEpAddr))
+	}
+	got := pm.relayEpAddrByNodeKey[nk]
+	if got != relayEpAddrB {
+		t.Fatalf("expected relay epAddr %v, got: %v", relayEpAddrB, got)
+	}
+}