RDMA/hns: Modify variable/field name from vlan to vlan_id

The name of vlan and vlan_tag is not clear enough, it's actually means
vlan id.

Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Link: https://lore.kernel.org/r/1567566885-23088-4-git-send-email-liweihang@hisilicon.com


Signed-off-by: Doug Ledford <dledford@redhat.com>