wireless: align HE capabilities A-MPDU Length Exponent Extension

The A-MPDU length exponent extension is defined differently in
802.11ax D6.1, align with that.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210409123755.c2a257d3e2df.I3455245d388c52c61dace7e7958dbed7e807cfb6@changeid


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