[iscsi] Include 802.1Q VLAN identifier in iBFT

The iBFT NIC section has a VLAN field which must be filled in so that
iSCSI booting works over VLANs.

Unfortunately it is unclear from the IBM specification linked in
ibft.c whether the VLAN field is just the 802.1Q VLAN Identifier or
the full 802.1Q TCI.  For now just fill in the VID, the Priority Code
Point and Drop Eligible Indicator could be set in the future if it
turns out they should be present too.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/block/ibft.c

 #include <ipxe/in.h>
 #include <ipxe/netdevice.h>
 #include <ipxe/ethernet.h>
+#include <ipxe/vlan.h>
 #include <ipxe/dhcp.h>
 #include <ipxe/iscsi.h>
 #include <ipxe/ibft.h>
 	DBG ( "iBFT NIC subnet = /%d\n", nic->subnet_mask_prefix );
 
 	/* Extract values from net-device configuration */
+	nic->vlan = cpu_to_le16 ( vlan_tag ( netdev ) );
+	DBG ( "iBFT NIC VLAN = %02x\n", le16_to_cpu ( nic->vlan ) );
 	if ( ( rc = ll_protocol->eth_addr ( netdev->ll_addr,
 					    nic->mac_address ) ) != 0 ) {
 		DBG ( "Could not determine iBFT MAC: %s\n", strerror ( rc ) );