nbd/server: avoid per-NBDRequest nbd_client_get/put()

nbd_trip() processes a single NBD request from start to finish and holds
an NBDClient reference throughout. NBDRequest does not outlive the scope
of nbd_trip(). Therefore it is unnecessary to ref/unref NBDClient for
each NBDRequest.

Removing these nbd_client_get()/nbd_client_put() calls will make
thread-safety easier in the commits that follow.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20231221192452.1785567-5-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

nbd/server.c

@@ -1557,7 +1557,6 @@ static NBDRequestData *nbd_request_get(NBDClient *client)
     client->nb_requests++;
 
     req = g_new0(NBDRequestData, 1);
-    nbd_client_get(client);
     req->client = client;
     return req;
 }
@@ -1578,8 +1577,6 @@ static void nbd_request_put(NBDRequestData *req)
     }
 
     nbd_client_receive_next_request(client);
-
-    nbd_client_put(client);
 }
 
 static void blk_aio_attached(AioContext *ctx, void *opaque)