IB/core: Enable WQ creation and modification with cvlan offload

Enable WQ creation and modification with cvlan stripping offload.
This includes:
- Adding WQ creation flags.
- Extending modify WQ to get flags and flags mask to enable turning
  it on and off.

Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>