ipn, wgengine: plumb NetworkMap down to magicsock

Now we can have magicsock make decisions based on tailcfg.Debug
settings sent by the server.

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

wgengine/wgengine.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/tailscale/wireguard-go/wgcfg"
+	"tailscale.com/control/controlclient"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/key"
@@ -105,6 +106,13 @@ type Engine interface {
 	// is configured.
 	SetDERPMap(*tailcfg.DERPMap)
 
+	// SetNetworkMap informs the engine of the latest network map
+	// from the server. The network map's DERPMap field should be
+	// ignored as as it might be disabled; get it from SetDERPMap
+	// instead.
+	// The network map should only be read from.
+	SetNetworkMap(*controlclient.NetworkMap)
+
 	// SetNetInfoCallback sets the function to call when a
 	// new NetInfo summary is available.
 	SetNetInfoCallback(NetInfoCallback)