iwlwifi: mvm: set max amsdu for TLC offload

mac80211 sets max amsdu to min supported ht vs vht but TLC only works
with one mode so we can set to the exact mode used (vht/ht)
and enable larger amsdu sizes for vht.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>