iwlwifi: mvm: treat MMPDUs in iwl_mvm_mac_tx() as bcast

There's no need for all the complicated conditions here, any
bufferable MMPDUs or MMPDUs for client interfaces are already
coming through the TXQ interface, not iwl_mvm_mac_tx().

Simplify the logic.

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.20210802172232.3939f7c5c43a.I1d5cb5262e31a000023d79acbb897b8db50adf0d@changeid


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