i2ptunnel: Use readonly, not disable, to avoid losing data in forms

Fix disabling of interface select box
Caused by disable changes on May 8

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 18;
+    public final static long BUILD = 19;
 
     /** for example "-test" */
     public final static String EXTRA = "";