selftests/bpf: Test auto-load disabling logic for BPF programs

Validate that BPF object with broken (in multiple ways) BPF program can still
be successfully loaded, if that broken BPF program is disabled.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200625232629.3444003-3-andriin@fb.com