feature/portmapper: make the portmapper & its debugging tools modular

Starting at a minimal binary and adding one feature back...
    tailscaled tailscale combined (linux/amd64)
     30073135  17451704  31543692 omitting everything
    +  480302 +   10258 +  493896 .. add debugportmapper
    +  475317 +  151943 +  467660 .. add portmapper
    +  500086 +  162873 +  510511 .. add portmapper+debugportmapper

Fixes #17148

Change-Id: I90bd0e9d1bd8cbe64fa2e885e9afef8fb5ee74b1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -6780,6 +6780,11 @@ func (b *LocalBackend) ControlKnobs() *controlknobs.Knobs {
 	return b.sys.ControlKnobs()
 }
 
+// EventBus returns the node's event bus.
+func (b *LocalBackend) EventBus() *eventbus.Bus {
+	return b.sys.Bus.Get()
+}
+
 // MagicConn returns the backend's *magicsock.Conn.
 func (b *LocalBackend) MagicConn() *magicsock.Conn {
 	return b.sys.MagicSock.Get()

ipn/ipnlocal/local_test.go

@@ -34,6 +34,7 @@ import (
 	"tailscale.com/control/controlclient"
 	"tailscale.com/drive"
 	"tailscale.com/drive/driveimpl"
+	_ "tailscale.com/feature/condregister/portmapper"
 	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"