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

Patch by Serhiy Storchaka.

diff --cc Lib/smtplib.py
index d37b0e247dd4e3460eb00df9eb4166e4d9de8375,e06a9be7413abf9b9441c1f723141297628a9401..c949d77b513f622bea90678f26792726317aab88
--- 1/Lib/smtplib.py
--- 2/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@@ -918,9 -891,8 +918,9 @@@ class LMTP(SMTP)
          # Handle Unix-domain sockets.
          try:
              self.sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
 +            self.file = None
              self.sock.connect(host)
-         except socket.error as msg:
+         except socket.error:
              if self.debuglevel > 0:
                  print('connect fail:', host, file=stderr)
              if self.sock: