derp: remove OnlyDisco option.

Active discovery lets us introspect the state of the network stack precisely
enough that it's unnecessary, and dropping the initial DERP packets greatly
slows down tests. Additionally, it's unrealistic since our production network
will never deliver _only_ discovery packets, it'll be all or nothing.

Signed-off-by: David Anderson <danderson@tailscale.com>

derp/derp_server.go

@@ -26,7 +26,6 @@ import (
 
 	"golang.org/x/crypto/nacl/box"
 	"golang.org/x/sync/errgroup"
-	"tailscale.com/disco"
 	"tailscale.com/metrics"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
@@ -52,13 +51,6 @@ type Server struct {
 	// before failing when writing to a client.
 	WriteTimeout time.Duration
 
-	// OnlyDisco controls whether, for tests, non-discovery packets
-	// are dropped. This is used by magicsock tests to verify that
-	// NAT traversal works (using DERP for out-of-band messaging)
-	// but the packets themselves aren't going via DERP.
-	OnlyDisco bool
-	_         [pad32bit]byte
-
 	privateKey key.Private
 	publicKey  key.Public
 	logf       logger.Logf
@@ -559,11 +551,6 @@ func (c *sclient) handleFrameSendPacket(ft frameType, fl uint32) error {
 		return fmt.Errorf("client %x: recvPacket: %v", c.key, err)
 	}
 
-	if s.OnlyDisco && !disco.LooksLikeDiscoWrapper(contents) {
-		s.packetsDropped.Add(1)
-		return nil
-	}
-
 	var fwd PacketForwarder
 	s.mu.Lock()
 	dst := s.clients[dstKey]

wgengine/magicsock/magicsock_test.go

@@ -69,11 +69,6 @@ func runDERPAndStun(t *testing.T, logf logger.Logf, l nettype.PacketListener, st
 		t.Fatal(err)
 	}
 	d := derp.NewServer(serverPrivateKey, logf)
-	if l != (nettype.Std{}) {
-		// When using virtual networking, only allow DERP to forward
-		// discovery traffic, not actual packets.
-		d.OnlyDisco = false
-	}
 
 	httpsrv := httptest.NewUnstartedServer(derphttp.Handler(d))
 	httpsrv.Config.ErrorLog = logger.StdLogger(logf)