Issue #5715: In socketserver, close the server socket in the child process.

Lib/socketserver.py

@@ -529,10 +529,10 @@ class ForkingMixIn:
                 self.active_children = []
             self.active_children.append(pid)
             self.close_request(request)
-            return
         else:
             # Child process.
             # This must never return, hence os._exit()!
+            self.socket.close()
             try:
                 self.finish_request(request, client_address)
                 os._exit(0)