cnic: Update VLAN ID during ISCSI_UEVENT_PATH_UPDATE

This will support the new VLAN attribute in the iSCSI iface file.

Signed-off-by: Eddie Wai <eddie.wai@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>