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

Enable user space application via WQ creation and modification to
turn on and off cvlan offload.

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>