IB: Add protocol for USNIC

Add protocol definition for the proprietary the USNIC driver.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>