RDMA/bnxt_re: Add vlan tag for untagged RoCE traffic when PFC is configured

Current implementation does not program vlan header insertion
in RoCE packet if no vlan is configured. Firmware does not add
prority when there is no vlan tag in the packet. Modify the code
to insert vlan header when PFC is enabled on the interface.

Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>