selftests/bpf: Fix test_verifier failed test in unprivileged mode

selftests/bpf: Fix test_verifier failed test in unprivileged mode

Loading the BTF won't be permitted without privileges, hence only test
for privileged mode by setting the prog type. This makes the
test_verifier show 0 failures when unprivileged BPF is enabled.

Fixes: 41188e9e9def ("selftest/bpf: Test for use-after-free bug fix in inline_bpf_loop")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220721134245.2450-14-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>