selftests/hid: add test for attaching multiple time the same struct_ops

Turns out that we would en up in a bad state if we attempt to attach
twice the same HID-BPF struct_ops, so have a test for it.

Link: https://patch.msgid.link/20240723-fix-6-11-bpf-v1-4-b9d770346784@kernel.org


Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>