ieee80211: bump IEEE80211_MAX_AMPDU_BUF to support HE

Bump the IEEE80211_MAX_AMPDU_BUF size to 0x100 for HE support
and - for now - use IEEE80211_MAX_AMPDU_BUF_HT everywhere.

This is derived from my internal patch, parts of which Luca
had sent upstream.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>