network: cancel netlink calls for detached requests

Store the asynchronous netlink slot in the Request object and release it
when the request is detached. This cancels the pending callback instead of
keeping the request alive until its reply arrives.

Follow-up for 80d62d4f1a

src/network/networkd-queue.c

@@ -22,6 +22,7 @@ static Request* request_detach_impl(Request *req) {
 
         ordered_set_remove(req->manager->request_queue, req);
         req->manager = NULL;
+        req->netlink_slot = sd_netlink_slot_unref(req->netlink_slot);
         return req;
 }
 
@@ -328,6 +329,10 @@ int manager_process_requests(Manager *manager) {
 static int request_netlink_handler(sd_netlink *nl, sd_netlink_message *m, Request *req) {
         assert(req);
 
+        assert(req->netlink_slot);
+        assert_se(sd_netlink_slot_set_floating(req->netlink_slot, true) >= 0);
+        req->netlink_slot = sd_netlink_slot_unref(req->netlink_slot);
+
         if (req->counter) {
                 assert(*req->counter > 0);
                 (*req->counter)--;
@@ -350,7 +355,7 @@ int request_call_netlink_async(sd_netlink *nl, sd_netlink_message *m, Request *r
         assert(m);
         assert(req);
 
-        r = netlink_call_async(nl, NULL, m, request_netlink_handler, request_destroy_callback, req);
+        r = netlink_call_async(nl, &req->netlink_slot, m, request_netlink_handler, request_destroy_callback, req);
         if (r < 0)
                 return r;