selftests: bpf: crypto skcipher algo selftests

Add simple tc hook selftests to show the way to work with new crypto
BPF API. Some tricky dynptr initialization is used to provide empty iv
dynptr. Simple AES-ECB algo is used to demonstrate encryption and
decryption of fixed size buffers.

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Link: https://lore.kernel.org/r/20240422225024.2847039-4-vadfed@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>