crush: add SET_CHOOSELEAF_VARY_R step

This lets you adjust the vary_r tunable on a per-rule basis.

Reflects ceph.git commit f944ccc20aee60a7d8da7e405ec75ad1cd449fac.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

diff --cc include/linux/crush/crush.h
Simple merge

diff --cc net/ceph/crush/mapper.c
Simple merge