IB/core: Add support for flow counters

A counters object could be attached to flow on creation by providing the
counter specification action.

General counters description which count packets and bytes are introduced,
downstream patches from this series will use them as part of flow counters
binding.

In addition, increase number of flow specifications supported layers to 10
upon adding count specification and for the previously added drop
specification.

Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>