iwlwifi: pcie: don't reset the TX queue counter

A few NICs can get into trouble if we reset the TX queue
counters in certain very rare situation. To be on the safe
side, simply avoid to reset the TX queue counter.
This is relevant for non-AMPDU queues only since on AMPDU
we have no choice - we must start the TX queue at the right
index.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>