selftests/bpf: Test bpf_program__clone() attach_btf_id override

selftests/bpf: Test bpf_program__clone() attach_btf_id override

Add a test that verifies bpf_program__clone() respects caller-provided
attach_btf_id in bpf_prog_load_opts.

The BPF program has SEC("fentry/bpf_fentry_test1"). It is cloned twice
from the same prepared object: first with no opts, verifying the
callback resolves attach_btf_id from sec_name to bpf_fentry_test1;
then with attach_btf_id overridden to bpf_fentry_test2, verifying the
loaded program is actually attached to bpf_fentry_test2. Both results
are checked via bpf_prog_get_info_by_fd().

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260317-veristat_prepare-v4-3-74193d4cc9d9@meta.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>