ipn/localapi: add debug handler to Rebind, ReSTUN magicsock

And more later probably.

Updates #3619

Change-Id: Ia4cba34a7c0dcce4d2eddec8aae17f32b51c207f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -55,6 +55,7 @@ import (
 	"tailscale.com/version/distro"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/filter"
+	"tailscale.com/wgengine/magicsock"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/wgcfg"
 	"tailscale.com/wgengine/wgcfg/nmcfg"
@@ -3138,3 +3139,33 @@ func exitNodeCanProxyDNS(nm *netmap.NetworkMap, exitNodeID tailcfg.StableNodeID)
 	}
 	return "", false
 }
+
+func (b *LocalBackend) DebugRebind() error {
+	mc, err := b.magicConn()
+	if err != nil {
+		return err
+	}
+	mc.Rebind()
+	return nil
+}
+
+func (b *LocalBackend) DebugReSTUN() error {
+	mc, err := b.magicConn()
+	if err != nil {
+		return err
+	}
+	mc.ReSTUN("explicit-debug")
+	return nil
+}
+
+func (b *LocalBackend) magicConn() (*magicsock.Conn, error) {
+	ig, ok := b.e.(wgengine.InternalsGetter)
+	if !ok {
+		return nil, errors.New("engine isn't InternalsGetter")
+	}
+	_, mc, ok := ig.GetInternals()
+	if !ok {
+		return nil, errors.New("failed to get internals")
+	}
+	return mc, nil
+}