iwlwifi: mvm: don't send fetch the TID from a non-QoS packet in TSO

Getting the TID of a packet before we know it is a QoS data
packet isn't a good idea. Delay the TID retrieval until
we know the packet is a QoS data packet.

Fixes: bb81bb68 ("iwlwifi: mvm: add Tx A-MSDU inside A-MPDU")
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>