selftests/bpf: Update task local data license

Change the license of task local data mini library to LGPL-2.1 or
BSD-2-Clause to allow it being in a wider range of projects.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260219225849.2426421-1-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>