feature/capture: move packet capture to feature/*, out of iOS + CLI

We had the debug packet capture code + Lua dissector in the CLI + the
iOS app. Now we don't, with tests to lock it in.

As a bonus, tailscale.com/net/packet and tailscale.com/net/flowtrack
no longer appear in the CLI's binary either.

A new build tag ts_omit_capture disables the packet capture code and
was added to build_dist.sh's --extra-small mode.

Updates #12614

Change-Id: I79b0628c0d59911bd4d510c732284d97b0160f10
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/tstun/wrap_test.go

@@ -40,7 +40,6 @@ import (
 	"tailscale.com/types/views"
 	"tailscale.com/util/must"
 	"tailscale.com/util/usermetric"
-	"tailscale.com/wgengine/capture"
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/wgcfg"
 )
@@ -871,14 +870,14 @@ func TestPeerCfg_NAT(t *testing.T) {
 // with the correct parameters when various packet operations are performed.
 func TestCaptureHook(t *testing.T) {
 	type captureRecord struct {
-		path capture.Path
+		path packet.CapturePath
 		now  time.Time
 		pkt  []byte
 		meta packet.CaptureMeta
 	}
 
 	var captured []captureRecord
-	hook := func(path capture.Path, now time.Time, pkt []byte, meta packet.CaptureMeta) {
+	hook := func(path packet.CapturePath, now time.Time, pkt []byte, meta packet.CaptureMeta) {
 		captured = append(captured, captureRecord{
 			path: path,
 			now:  now,
@@ -935,19 +934,19 @@ func TestCaptureHook(t *testing.T) {
 	// Assert that the right packets are captured.
 	want := []captureRecord{
 		{
-			path: capture.FromPeer,
+			path: packet.FromPeer,
 			pkt:  []byte("Write1"),
 		},
 		{
-			path: capture.FromPeer,
+			path: packet.FromPeer,
 			pkt:  []byte("Write2"),
 		},
 		{
-			path: capture.SynthesizedToLocal,
+			path: packet.SynthesizedToLocal,
 			pkt:  []byte("InjectInboundPacketBuffer"),
 		},
 		{
-			path: capture.SynthesizedToPeer,
+			path: packet.SynthesizedToPeer,
 			pkt:  []byte("InjectOutboundPacketBuffer"),
 		},
 	}