mac80211: calculate max RX NSS for EHT mode

If the station supports EHT mode, calculate the maximum RX NSS
from EHT station capabilities.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Link: https://lore.kernel.org/r/20220214173004.cf61972c8919.I54f5a416f0789bf4eefad04703d941b6755f6dd6@changeid


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