never ignore a (potential) tunnel failure, even though the tunnel may not have failed

(e.g. test outbound through A with a reply inbound through B.  if the message is lost, which tunnel failed?  both!)

router/java/src/net/i2p/router/tunnelmanager/TunnelPool.java

@@ -524,7 +524,7 @@ class TunnelPool {
         return found;
     }
     
-    private static final int MAX_FAILURES_PER_TUNNEL = 2;
+    private static final int MAX_FAILURES_PER_TUNNEL = 0;
     
     public void tunnelFailed(TunnelId id) {
         if (!_isLive) return;