Mark port as non-listening

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -336,6 +336,8 @@ cdef extern from "grpc/_cython/loader.h":
   void grpc_server_register_completion_queue(grpc_server *server,
                                              grpc_completion_queue *cq,
                                              void *reserved) nogil
+  void grpc_server_register_non_listening_completion_queue(
+      grpc_server *server, grpc_completion_queue *cq, void *reserved) nogil
   int grpc_server_add_insecure_http2_port(
       grpc_server *server, const char *addr) nogil
   void grpc_server_start(grpc_server *server) nogil

src/python/grpcio/grpc/_cython/_cygrpc/server.pyx.pxi

@@ -81,11 +81,20 @@ cdef class Server:
           self.c_server, queue.c_completion_queue, NULL)
     self.registered_completion_queues.append(queue)
 
+  def register_non_listening_completion_queue(
+      self, CompletionQueue queue not None):
+    if self.is_started:
+      raise ValueError("cannot register completion queues after start")
+    with nogil:
+      grpc_server_register_non_listening_completion_queue(
+          self.c_server, queue.c_completion_queue, NULL)
+    self.registered_completion_queues.append(queue)
+
   def start(self):
     if self.is_started:
       raise ValueError("the server has already started")
     self.backup_shutdown_queue = CompletionQueue()
-    self.register_completion_queue(self.backup_shutdown_queue)
+    self.register_non_listening_completion_queue(self.backup_shutdown_queue)
     self.is_started = True
     with nogil:
       grpc_server_start(self.c_server)
@@ -169,4 +178,3 @@ cdef class Server:
           time.sleep(0)
       with nogil:
         grpc_server_destroy(self.c_server)
-