Move session support check into server selection for unified topology

Author: nbbeeken

lib/operations/execute_operation.js

@@ -142,6 +142,10 @@ function executeWithServerSelection(topology, operation, callback) {
       return;
     }
 
+    if (serverSelectionOptions.session && topology.hasSessionSupport()) {
+      return callback(new MongoError('Current topology does not support sessions'));
+    }
+
     const shouldRetryReads =
       topology.s.options.retryReads !== false &&
       operation.session &&