udev/watch: drop inotify fd from fdstore if exists

Otherwise, if an inotify fd stored in the fdstore but we could not get
it for some reasons, fdstore will store multiple inotify fds.
For safety, let's always remove existing inotify fds in fdstore when we
initialized new one.

Follow-up for beaf7e04eb.

src/udev/udev-manager.c

@@ -1166,7 +1166,7 @@ static int manager_listen_fds(Manager *manager) {
 
         int n = sd_listen_fds_with_names(/* unset_environment = */ true, &names);
         if (n < 0)
-                return n;
+                return log_error_errno(n, "Failed to listen on fds: %m");
 
         for (int i = 0; i < n; i++) {
                 int fd = SD_LISTEN_FDS_START + i;

src/udev/udev-watch.c

@@ -360,6 +360,7 @@ int manager_init_inotify(Manager *manager, int fd) {
         manager->inotify_fd = fd;
         (void) udev_watch_restore(manager);
 
+        (void) notify_remove_fd_warn("inotify");
         r = notify_push_fd(manager->inotify_fd, "inotify");
         if (r < 0)
                 log_warning_errno(r, "Failed to push inotify fd to service manager, ignoring: %m");