iwlwifi: mvm: rs-fw: handle VHT extended NSS capability

If extended NSS capability is used, the NSS for 160 may be
lower than for 80.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200911204056.523f5eca82ce.Ic0cd9cc86a91b1f23a5a54921736332be9abac29@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>