i40e: clear qtx_head before enabling Tx queue
i40e: clear qtx_head before enabling Tx queue

Make sure the "new" qtx_head[q] register is cleared before
enabling the Tx queue.

Change-ID: I0c7a12815e343a5ae68807af172a35d6c6857935
Signed-off-by: Shannon Nelson <14bbe8f00ad7c6d888a504d41f5500c00531af99@intel.com>
Signed-off-by: Jesse Brandeburg <e6047e445db6578741afb14ef640164ef6b65e4f@intel.com>
Tested-by: Kavindya Deegala <0716ac131ef4b886955b7082f827ccaacb3c2837@intel.com>
Signed-off-by: Jeff Kirsher <87e35f5be20bb3e67f4ba6b86f5f6be3085b1b3a@intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs