[thunderx] Fix hardware deinitialization

It is required to reset BGX context state for the LMAC using
BGX_CMR_CONFIG register.

This solves problem with network connectivity in Linux booted from
iPXE.

Signed-off-by: Bartosz Szczepanek <bartosz.szczepanek@cavium.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/thunderx.c

  * @v lmac		Logical MAC
  */
 static void txnic_lmac_remove ( struct txnic_lmac *lmac ) {
+	uint64_t config;
 
 	/* Sanity check */
 	assert ( lmac->vnic != NULL );
 
+	/* Disable packet receive and transmit */
+	config = readq ( lmac->regs + BGX_CMR_CONFIG );
+	config &= ~( BGX_CMR_CONFIG_DATA_PKT_TX_EN |
+		     BGX_CMR_CONFIG_DATA_PKT_RX_EN );
+	writeq ( config, ( lmac->regs + BGX_CMR_CONFIG ) );
+
 	/* Unregister network device */
 	unregister_netdev ( lmac->vnic->netdev );