cmd/tailscale,ipn/ipnlocal: enable web client over quad 100 by default (#11419)

Enable the web client over 100.100.100.100 by default. Accepting traffic
from [tailnet IP]:5252 still requires setting the `webclient` user pref.

Updates https://github.com/tailscale/tailscale/issues/10261

Signed-off-by: Mario Minardi <mario@tailscale.com>

ipn/prefs.go

@@ -118,7 +118,8 @@ type Prefs struct {
 	// policies as configured by the Tailnet's admin(s).
 	RunSSH bool
 
-	// RunWebClient bool is whether this node should run a web client,
+	// RunWebClient bool is whether this node should expose
+	// its web client over Tailscale at port 5252,
 	// permitting access to peers according to the
 	// policies as configured by the Tailnet's admin(s).
 	RunWebClient bool