IB/mlx5: Add flow tag support

Set flow tag in flow table entry, when IB_FLOW_SPEC_ACTION_TAG
is part of the flow specifications.

Flow tag doesn't support multicast flows, so it's passing to
hardware only when used.

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