[improvement](filecache)Change the hash field of the backend (#17499)

ip of backend may change
use id as a hash field

fe/fe-core/src/main/java/org/apache/doris/qe/Coordinator.java

@@ -267,8 +267,7 @@ public class Coordinator {
     private static class BackendHash implements Funnel<Backend> {
         @Override
         public void funnel(Backend backend, PrimitiveSink primitiveSink) {
-            primitiveSink.putBytes(backend.getIp().getBytes(StandardCharsets.UTF_8));
-            primitiveSink.putInt(backend.getBePort());
+            primitiveSink.putLong(backend.getId());
         }
     }