ipn,tsnet: update AdvertiseTags documentation (#16931)

Instead of referring to groups, which is a term of art for a different entity,
update the doc comments to more accurately describe what tags are in reference
to the policy document.

Updates #cleanup

Change-Id: Iefff6f84981985f834bae7c6a6c34044f53f2ea2
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>

ipn/prefs.go

@@ -158,11 +158,10 @@ type Prefs struct {
 	// connections. This overrides tailcfg.Hostinfo's ShieldsUp.
 	ShieldsUp bool
 
-	// AdvertiseTags specifies groups that this node wants to join, for
+	// AdvertiseTags specifies tags that should be applied to this node, for
-	// purposes of ACL enforcement. These can be referenced from the ACL
+	// purposes of ACL enforcement. These can be referenced from the ACL policy
-	// security policy. Note that advertising a tag doesn't guarantee that
+	// document. Note that advertising a tag on the client doesn't guarantee
-	// the control server will allow you to take on the rights for that
+	// that the control server will allow the node to adopt that tag.
-	// tag.
 	AdvertiseTags []string
 
 	// Hostname is the hostname to use for identifying the node. If

tsnet/tsnet.go

@@ -124,11 +124,10 @@ type Server struct {
 	// field at zero unless you know what you are doing.
 	Port uint16
 
-	// AdvertiseTags specifies groups that this embedded server wants to join, for
+	// AdvertiseTags specifies tags that should be applied to this node, for
-	// purposes of ACL enforcement. These can be referenced from the ACL
+	// purposes of ACL enforcement. These can be referenced from the ACL policy
-	// security policy. Note that advertising a tag doesn't guarantee that
+	// document. Note that advertising a tag on the client doesn't guarantee
-	// the control server will allow you to take on the rights for that
+	// that the control server will allow the node to adopt that tag.
-	// tag.
 	AdvertiseTags []string
 
 	getCertForTesting func(*tls.ClientHelloInfo) (*tls.Certificate, error)