Tunnels: Improve expl. build success in well-connected routers during congestion

by not using high cap tier. Congestion starts from the top.
Right now, the fastest routers have the worst expl. build success.
This will help correct that.

router/java/src/net/i2p/router/tunnel/pool/ExploratoryPeerSelector.java

@@ -275,6 +275,11 @@ class ExploratoryPeerSelector extends TunnelPeerSelector {
         if (uptime <= 11*60*1000) {
             failPct = 100 - MIN_NONFAILING_PCT;
         } else {
+            // If well connected or ff, don't pick from high cap
+            // even during congestion, because congestion starts from the top
+            if (active > 500 || ctx.netDb().floodfillEnabled())
+                return false;
+
             failPct = getExploratoryFailPercentage();
             //Log l = ctx.logManager().getLog(getClass());
             //if (l.shouldLog(Log.DEBUG))