loadbalancer-experimental: assert a lock instead of comment about it (#…

…2857)

Motivation:

An assert is worth a thousand comments.

Modifications:

Replace the comment about holding the lock in DefaultRequestTracker
with an assert.

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/DefaultRequestTracker.java

@@ -173,8 +173,8 @@ private static int applyPenalty(int currentEWMA, int currentLatency, long penalt
         return (int) min(MAX_VALUE, max(currentEWMA, currentLatency) * penalty);
     }
 
-    // must be called while holding the lock in write mode.
     private void updateEwma(long penalty, long startTimeNanos) {
+        assert lock.isWriteLocked();
         // We capture the current time while holding the lock to exploit the monotonic time source
         // properties which prevent the time duration from going negative. This will result in a latency penalty
         // as concurrency increases, but is a trade-off for simplicity.