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/test/test-bpf-foreign-programs.c

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: LGPL-2.1+ */
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #include <fcntl.h>
 #include <linux/bpf_insn.h>