selftests/bpf: Add test for alu on PTR_TO_FLOW_KEYS

Add a test case for PTR_TO_FLOW_KEYS alu. Testing if alu with variable
offset on flow_keys is rejected. For the fixed offset success case, we
already have C code coverage to verify (e.g. via bpf_flow.c).

Signed-off-by: Hao Sun <sunhao.th@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240115082028.9992-2-sunhao.th@gmail.com

selftests/bpf: verifier/value_illegal_alu converted to inline assembly

Test verifier/value_illegal_alu automatically converted to use inline assembly.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230421174234.2391278-24-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>