iwlwifi: pcie: use don't disable interrupt when rxq->lock is taken

This lock was never acquired in the primary interrupt
handler, but since it was acquired along with irq_lock
which had to disable interrupts, rxq->lock had to disable
interrupts too.
Now that trans_pcie->irq_lock isn't acquired in the primary
interrupt handler, rxq->lock can let interrupt enabled.

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