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>

cmd/tailscale/cli/cli_test.go

@@ -25,10 +25,12 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/tka"
 	"tailscale.com/tstest"
+	"tailscale.com/tstest/deptest"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/opt"
 	"tailscale.com/types/persist"
 	"tailscale.com/types/preftype"
+	"tailscale.com/util/set"
 	"tailscale.com/version/distro"
 )
 
@@ -1568,3 +1570,31 @@ func TestDocs(t *testing.T) {
 	}
 	walk(t, root)
 }
+
+func TestDeps(t *testing.T) {
+	deptest.DepChecker{
+		GOOS:   "linux",
+		GOARCH: "arm64",
+		WantDeps: set.Of(
+			"tailscale.com/feature/capture/dissector", // want the Lua by default
+		),
+		BadDeps: map[string]string{
+			"tailscale.com/feature/capture": "don't link capture code",
+			"tailscale.com/net/packet":      "why we passing packets in the CLI?",
+			"tailscale.com/net/flowtrack":   "why we tracking flows in the CLI?",
+		},
+	}.Check(t)
+}
+
+func TestDepsNoCapture(t *testing.T) {
+	deptest.DepChecker{
+		GOOS:   "linux",
+		GOARCH: "arm64",
+		Tags:   "ts_omit_capture",
+		BadDeps: map[string]string{
+			"tailscale.com/feature/capture":           "don't link capture code",
+			"tailscale.com/feature/capture/dissector": "don't like the Lua",
+		},
+	}.Check(t)
+
+}