patch 8.2.4690: channel tests fail on MS-Windows

Problem:    Channel tests fail on MS-Windows.
Solution:   Check if the AF_UNIX attribute exists. (closes #10083)
diff --git a/src/testdir/test_channel.py b/src/testdir/test_channel.py
index b0c3140..3ef0fde 100644
--- a/src/testdir/test_channel.py
+++ b/src/testdir/test_channel.py
@@ -19,12 +19,7 @@
     # Python 2
     import SocketServer as socketserver
 
-class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):
-
-    def setup(self):
-        if self.server.address_family != socket.AF_UNIX:
-            self.request.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
-
+class TestingRequestHandler(socketserver.BaseRequestHandler):
     def handle(self):
         print("=== socket opened ===")
         while True:
@@ -240,6 +235,10 @@
                 elif decoded[0] < 0:
                     last_eval = decoded
 
+class ThreadedTCPRequestHandler(TestingRequestHandler):
+    def setup(self):
+        self.request.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+
 class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
     pass