Issue #16647: save socket error details in LMTP.connect()

Initial patch by Serhiy Storchaka.
diff --git a/Lib/test/mock_socket.py b/Lib/test/mock_socket.py
index d09e78c..8ef0ec8 100644
--- a/Lib/test/mock_socket.py
+++ b/Lib/test/mock_socket.py
@@ -140,12 +140,8 @@
     return ""
 
 
-class gaierror(Exception):
-    pass
-
-
-class error(Exception):
-    pass
+gaierror = socket_module.gaierror
+error = socket_module.error
 
 
 # Constants