MINOR: cpu-topo: also store the sibling ID with SMT

MINOR: cpu-topo: also store the sibling ID with SMT

The sibling ID was not reported because it's not directly accessible
but we don't care, what matters is that we assign numbers to all the
threads we find using the same CPU so that some strategies permit to
allocate one thread at a time if we want to use few threads with max
performance.