IB/core: Introduce flow tag specification

This specification identifies flow with a specific tag-id.
This tag-id will be reported in the CQE.

Signed-off-by: Moses Reuben <mosesr@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>