I see I left in a couple of unused variables, but I'm now questioning their purpose. KP, as the original author, can you explain the purpose of the `bpf_modify_return_test`? Since this function is running in the context of the bpf syscall and not the bpf program itself, how would the side effect of the addition operation (I guess simulating the attached function running) ever not happen? If we adopt actually running the BPF program, should there just be a check for setting the upper 16 bits to represent 'side effects'?
