ixl(4)/ixlv(4): Remove a couple unnecessary register writes/flushes.

The one in ixl_xmit() has brought up to us as being unnecessary at least a
couple times.

Differential Revision:	https://reviews.freebsd.org/D5208
Tested by:	jeffrey.e.pieper@intel.com
Sponsored by:	Intel Corporation

sys/dev/ixl/if_ixl.c

@@ -2912,7 +2912,6 @@ ixl_initialize_vsi(struct ixl_vsi *vsi)
 			device_printf(dev, "Fail in init_rx_ring %d\n", i);
 			break;
 		}
-		wr32(vsi->hw, I40E_QRX_TAIL(que->me), 0);
 #ifdef DEV_NETMAP
 		/* preserve queue */
 		if (vsi->ifp->if_capenable & IFCAP_NETMAP) {

sys/dev/ixl/ixl_txrx.c

@@ -390,7 +390,6 @@ ixl_xmit(struct ixl_queue *que, struct mbuf **m_headp)
 	++txr->total_packets;
 	wr32(hw, txr->tail, i);
 
-	ixl_flush(hw);
 	/* Mark outstanding work */
 	if (que->busy == 0)
 		que->busy = 1;