Re-enable parameter push thread in learner server

- Uncomment and start the param_push_thread
- Restore thread joining for param_push_thread

checkport.py

@@ -0,0 +1,18 @@
+import socket
+
+
+def check_port(host, port):
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    try:
+        s.connect((host, port))
+        print(f"Connection successful to {host}:{port}!")
+    except Exception as e:
+        print(f"Connection failed to {host}:{port}: {e}")
+    finally:
+        s.close()
+
+
+if __name__ == "__main__":
+    host = "127.0.0.1"  # or "localhost"
+    port = 51350
+    check_port(host, port)