IB/rxe: support for 802.1q VLAN on the listener

Set the vlan flag and vlan_id field in the wc for rdma_listen()
to work over VLAN. This is required by ib_init_ah_attr_from_wc()
which is called by the CM REQ handler.

Signed-off-by: Vijay Immanuel <vijayi@attalasystems.com>
Reviewed-by: Yonatan Cohen <yonatanc@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>