Deferring sampling attempts to the second stage has some bad interactions
with drivers that process the rate table in hardware and use the probe flag
to indicate probing packets (e.g. most mt76 drivers). On affected drivers
it can lead to probing not working at all.

If the link conditions turn worse, it might not be such a good idea to
do a lot of sampling for lower rates in this case.

Fix this by simply skipping the sample attempt instead of deferring it,
but keep the checks that would allow it to be sampled if it was skipped
too often, but only if it has less than 95% success probability.

Also ensure that IEEE80211_TX_CTL_RATE_CTRL_PROBE is set for all probing
packets.

Cc: stable@vger.kernel.org
Fixes: cccf129f ("mac80211: add the 'minstrel' rate control algorithm")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20201111183359.43528-2-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>