bpo-40275: Move transient_internet from test.support to socket_helper (GH-19711)

diff --git a/Lib/test/test_smtpnet.py b/Lib/test/test_smtpnet.py
index b69cd9d..74a00a9 100644
--- a/Lib/test/test_smtpnet.py
+++ b/Lib/test/test_smtpnet.py
@@ -1,5 +1,6 @@
 import unittest
 from test import support
+from test.support import socket_helper
 import smtplib
 import socket
 
@@ -28,7 +29,7 @@
         context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
         context.check_hostname = False
         context.verify_mode = ssl.CERT_NONE
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             server = smtplib.SMTP(self.testServer, self.remotePort)
             try:
                 server.starttls(context=context)
@@ -47,14 +48,14 @@
 
     def test_connect(self):
         support.get_attribute(smtplib, 'SMTP_SSL')
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             server = smtplib.SMTP_SSL(self.testServer, self.remotePort)
             server.ehlo()
             server.quit()
 
     def test_connect_default_port(self):
         support.get_attribute(smtplib, 'SMTP_SSL')
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             server = smtplib.SMTP_SSL(self.testServer)
             server.ehlo()
             server.quit()
@@ -64,20 +65,20 @@
         context.check_hostname = False
         context.verify_mode = ssl.CERT_NONE
         support.get_attribute(smtplib, 'SMTP_SSL')
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             server = smtplib.SMTP_SSL(self.testServer, self.remotePort, context=context)
             server.ehlo()
             server.quit()
 
     def test_connect_using_sslcontext_verified(self):
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             can_verify = check_ssl_verifiy(self.testServer, self.remotePort)
             if not can_verify:
                 self.skipTest("SSL certificate can't be verified")
 
         support.get_attribute(smtplib, 'SMTP_SSL')
         context = ssl.create_default_context()
-        with support.transient_internet(self.testServer):
+        with socket_helper.transient_internet(self.testServer):
             server = smtplib.SMTP_SSL(self.testServer, self.remotePort, context=context)
             server.ehlo()
             server.quit()