tstest/integration/nat: add sameLAN node type

To test local connections.

Updates #13038

Change-Id: I575dcab31ca812edf7d04fa126772611cf89b9a7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/natlab/vnet/conf.go

@@ -33,6 +33,13 @@ func (c *Config) NumNodes() int {
 	return len(c.nodes)
 }
 
+func (c *Config) FirstNetwork() *Network {
+	if len(c.networks) == 0 {
+		return nil
+	}
+	return c.networks[0]
+}
+
 // AddNode creates a new node in the world.
 //
 // The opts may be of the following types:
@@ -145,6 +152,13 @@ type Network struct {
 	err error // carried error
 }
 
+func (n *Network) CanTakeMoreNodes() bool {
+	if n.natType == One2OneNAT {
+		return len(n.nodes) == 0
+	}
+	return len(n.nodes) < 150
+}
+
 // NetworkService is a service that can be added to a network.
 type NetworkService string