aya: Fix is_perf_link_supported

[dave-tucker]

This was mistakenly comparing the exit code of the syscall, which is always -1 and not the corresponding error-code. Added unit tests to ensure we don't regress.

Signed-off-by: Dave Tucker dave@dtucker.co.uk

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[dave-tucker]

Before:

bpf(BPF_LINK_CREATE, {link_create={prog_fd=11, target_fd=-1, attach_type=BPF_PERF_EVENT, flags=0, perf_event={bpf_cookie=0}}}, 144) = -1 EBADF (Bad file descriptor)
[2023-02-13T14:16:21Z DEBUG aya::bpf] BPF Feature Detection: Features {
        bpf_name: true,
        bpf_perf_link: false,
        btf: Some(
            BtfFeatures {
                btf_func: true,
                btf_func_global: true,
                btf_datasec: true,
                btf_float: true,
                btf_decl_tag: true,
                btf_type_tag: true,
            },
        ),
    }

After:

bpf(BPF_LINK_CREATE, {link_create={prog_fd=11, target_fd=-1, attach_type=BPF_PERF_EVENT, flags=0, perf_event={bpf_cookie=0}}}, 144) = -1 EBADF (Bad file descriptor)
[2023-02-13T14:36:22Z DEBUG aya::bpf] BPF Feature Detection: Features {
       bpf_name: true,
       bpf_perf_link: true,
       btf: Some(
           BtfFeatures {
               btf_func: true,
               btf_func_global: true,
               btf_datasec: true,
               btf_float: true,
               btf_decl_tag: true,
               btf_type_tag: true,
           },
       ),
   }

[dave-tucker]

Will merge on green since this is a smol bugfix 🤏 🐛