Pkg xen devel - Aug 2021 - backport tools/libxenstat: fix populating vbd.rd_sect

Dear maintainers,

Please consider backporting 
https://github.com/xen-project/xen/commit/c3cc6e206ff79c6117b841891d832694597bd5af
into libxenmisc4.14, if possible. It is a small change, that fixes vbd 
requests parsing.

Thanks,
Richard