xds: CHANNEL_ID hash should be random for the channel

The log id is an incrementing value starting from 0. That means the same
binary on two different machines will have the same hashes for each
consecutive Channel. That was not at all the intension of CHANNEL_ID.
From gRFC A42:

> This can be used in similar situations to where Envoy uses
> connection_properties to hash on the source IP address.

xds/src/main/java/io/grpc/xds/XdsNameResolver.java

@@ -123,6 +123,7 @@ final class XdsNameResolver extends NameResolver {
   // put()/remove() must be called in SyncContext, and get() can be called in any thread.
   private final ConcurrentMap<String, ClusterRefState> clusterRefs = new ConcurrentHashMap<>();
   private final ConfigSelector configSelector = new ConfigSelector();
+  private final long randomChannelId;
 
   private volatile RoutingConfig routingConfig = RoutingConfig.empty;
   private Listener2 listener;
@@ -162,6 +163,7 @@ final class XdsNameResolver extends NameResolver {
     this.xdsClientPoolFactory.setBootstrapOverride(bootstrapOverride);
     this.random = checkNotNull(random, "random");
     this.filterRegistry = checkNotNull(filterRegistry, "filterRegistry");
+    randomChannelId = random.nextLong();
     logId = InternalLogId.allocate("xds-resolver", name);
     logger = XdsLogger.withLogId(logId);
     logger.log(XdsLogLevel.INFO, "Created resolver for {0}", name);
@@ -586,7 +588,7 @@ private long generateHash(List<HashPolicy> hashPolicies, Metadata headers) {
             newHash = hashFunc.hashAsciiString(value);
           }
         } else if (policy.type() == HashPolicy.Type.CHANNEL_ID) {
-          newHash = hashFunc.hashLong(logId.getId());
+          newHash = hashFunc.hashLong(randomChannelId);
         }
         if (newHash != null ) {
           // Rotating the old value prevents duplicate hash rules from cancelling each other out

xds/src/test/java/io/grpc/xds/XdsNameResolverTest.java

@@ -802,6 +802,7 @@ public void resolved_rpcHashingByChannelId() {
     // A different resolver/Channel.
     resolver.shutdown();
     reset(mockListener);
+    when(mockRandom.nextLong()).thenReturn(123L);
     resolver = new XdsNameResolver(null, AUTHORITY, null, serviceConfigParser,
         syncContext, scheduler,
         xdsClientPoolFactory, mockRandom, FilterRegistry.getDefaultRegistry(), null);