bpf: add test cases for non-pointer sanitiation logic

Add two additional tests for further asserting the
BPF_ALU_NON_POINTER logic with cases that were missed
previously.

Cc: Marek Majkowski <marek@cloudflare.com>
Cc: Arthur Fabre <afabre@cloudflare.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>