fix routes not being saved when new nodes registers (#2444)

* add test to validate exitnode propagation

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* save routes on register

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* update changelog

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* no nil

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* add missing integration tests

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

integration/tsic/tsic.go

@@ -80,6 +80,7 @@ type TailscaleInContainer struct {
 	withExtraHosts    []string
 	workdir           string
 	netfilter         string
+	extraLoginArgs    []string
 
 	// build options, solely for HEAD
 	buildConfig TailscaleInContainerBuildConfig
@@ -203,6 +204,14 @@ func WithBuildTag(tag string) Option {
 	}
 }
 
+// WithExtraLoginArgs adds additional arguments to the `tailscale up` command
+// as part of the Login function.
+func WithExtraLoginArgs(args []string) Option {
+	return func(tsic *TailscaleInContainer) {
+		tsic.extraLoginArgs = args
+	}
+}
+
 // New returns a new TailscaleInContainer instance.
 func New(
 	pool *dockertest.Pool,
@@ -436,6 +445,10 @@ func (t *TailscaleInContainer) Login(
 		"--accept-routes=false",
 	}
 
+	if t.extraLoginArgs != nil {
+		command = append(command, t.extraLoginArgs...)
+	}
+
 	if t.withSSH {
 		command = append(command, "--ssh")
 	}
@@ -475,6 +488,10 @@ func (t *TailscaleInContainer) LoginWithURL(
 		"--accept-routes=false",
 	}
 
+	if t.extraLoginArgs != nil {
+		command = append(command, t.extraLoginArgs...)
+	}
+
 	stdout, stderr, err := t.Execute(command)
 	if errors.Is(err, errTailscaleNotLoggedIn) {
 		return nil, errTailscaleCannotUpWithoutAuthkey