mac80211: minstrel_ht: show sampling rates in debugfs

This makes it easier to see what rates are going to be tested next

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20210127055735.78599-5-nbd@nbd.name


Signed-off-by: Johannes Berg <johannes.berg@intel.com>