Transport: Raise bandwidth refiller thread priority

so I/O doesn't stall under high CPU load
- Raise DH generator thread priority to keep
  DH building out of event pumper thread
- Raise PRNG and YK generator thread priorites one notch
- Set I2PThread priority in constructor
Fixes problems mainly seen on Windows, which seems
to be much more sensitive to priority settings

router/java/src/net/i2p/router/transport/FIFOBandwidthLimiter.java

@@ -98,7 +98,7 @@ public class FIFOBandwidthLimiter {
         _lastStatsUpdated = now();
         _refiller = new FIFOBandwidthRefiller(_context, this);
         _refillerThread = new I2PThread(_refiller, "BWRefiller", true);
-        _refillerThread.setPriority(I2PThread.NORM_PRIORITY-1);
+        _refillerThread.setPriority(I2PThread.NORM_PRIORITY + 1);
         _refillerThread.start();
     }
 

router/java/src/net/i2p/router/transport/crypto/DHSessionKeyBuilder.java

@@ -470,7 +470,8 @@ public class DHSessionKeyBuilder {
                 _log.debug("DH Precalc (minimum: " + _minSize + " max: " + _maxSize + ", delay: "
                            + _calcDelay + ")");
             _builders = new LinkedBlockingQueue<DHSessionKeyBuilder>(_maxSize);
-            setPriority(Thread.MIN_PRIORITY);
+            if (!SystemVersion.isWindows())
+                setPriority(Thread.NORM_PRIORITY - 1);
         }
         
         /**