tree-wide: fix SPDX short identifier for LGPL-2.1-or-later

https://spdx.dev/ids/#:~:text=Allowing%20later%20versions%20of%20a%20license
https://spdx.org/licenses/LGPL-2.1-or-later.html

src/shared/bpf-link.c

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: LGPL-2.1+ */
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #include "bpf-dlopen.h"
 #include "bpf-link.h"

src/shared/bpf-link.h

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: LGPL-2.1+ */
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #pragma once