net: Fix namespace fd leak in get_socket_ns()

We open ns_fd via ioctl(SIOCGSKNS), but never close. Fix that.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/net.c

@@ -2701,8 +2701,10 @@ struct ns_id *get_socket_ns(int lfd)
 	}
 	if (fstat(ns_fd, &st)) {
 		pr_perror("Unable to stat a network namespace");
+		close(ns_fd);
 		return NULL;
 	}
+	close(ns_fd);
 
 	ns = lookup_ns_by_kid(st.st_ino, &net_ns_desc);
 	if (ns == NULL) {